People often express their dissatisfaction with others, this is very common in social life [7] . In the literature, the broadest definition of complaint is the expression of discontent, regardless of whether such discontent really exists or not [8] . Employee complaints are expressions of dissatisfaction with work and organization [9] .

In the process of providing products or services for consumers, front-line service employees working in the enterprise-consumer interface will inevitably have a large number of service contacts and interactions with consumers [1] . Service contact is the interaction between the customer and the service provider. The objects of service contact are not only limited to the interaction between the customer and the service provider, but also all other elements in the service delivery process that can affect the customer perception [10] [11] . Customer contact with frontline service employees includes both direct contact, such as complaints in front of customers, and indirect contact [5] , such as in clothing stores, employee complaints heard by customers in fitting room. Therefore, when front-line service employees complain in the workplace, even if the front-line service staff who complained about behavior did not interact with the consumer, the consumer can see and hear such complaints.

According to the third-party perception model of employee treatment, the organization’s treatment of employees will cause reactions from other colleagues, consumers, investors and other third parties [4] . Consumer witness front-line service employees complain that as a third party, they indirectly obtain information about how employees are treated through employee complaint content.

Previous studies have shown that third parties respond to the treatment of employees [12] [13] . The response is mainly based on the negative impact on employees and the attribution of responsibility after obtaining information [14] . People spontaneously attribute observed behaviors or events [15] [16] [17] , and classified into three dimensions: stability (behavior or occasional occurrence of behavior or events), attribution of responsibility (because of the responsibility of the company or the responsibility of the employee or the responsibility of other parties) and controllability (behavior) Or the cause of the event is that the enterprise can control or the enterprise is uncontrollable) (Weiner, 2000) [18] .

Based on responsibility attribution, the paper focuses on perceived enterprise controllability. This dimension will lead to the division of service failure into perceived high controllability factors and perceived low controllability factors. When consumers attribute service failure to high controllability factors, consumers believe that service failure is the enterprise can control. Less control is caused by uncontrolled [19] . When consumers attribute service failure to low controllability factors, that is, consumers believe that service failure is caused by uncontrollable and uncontrolled enterprises, and the satisfaction of enterprises is relatively high. From the consumer perception perspective, Liu verifies the influence of consumers’ controllability attribution on other customers’ inappropriate behaviors on satisfaction [20] . Albrecht based on the dimension of perceived controllability, the consumer perception of employee emotions (including positive emotions and negative emotions) is divided into the factors of perceived corporate controllability and perceived enterprise uncontrollability. When consumers perceive the cause of employee emotions, they are enterprises. When it is uncontrollable, whether the employee’s emotions are positive or negative, the consumer’s reaction is more favorable [21] .

Brand is defined as a relationship partner with its own personality from the perspective of service perception [22] [23] . Service brand is based on the relationship between customers and employees [24] . Therefore, the interaction between consumers and employees greatly affects the overall experience of consumers on the brand [25] .

The controllability dimension will affect the judgment of responsibility. The higher the consumer’s perceived controllability, the more judged the responsibility of the enterprise, the lower the consumer brand attitude [21] [26] . Based on previous research, Hypothesis 1 is proposed as follows:

H1: Witnessing the frontline service staff complained that the higher the controllability of the perceived business, the lower the consumer brand attitude.

According to the definition of employee complaints, the paper explores the source of employee complaints from the perspective of employee job satisfaction. Based on the two-factor theory, this paper divides perceived employee complaint sources into two categories: one is health care factors, that is, consumers perceive employee complaint sources as factors that enterprises must achieve, such as employee complaints about company deduction of wages, failure to implement effective supervision, inequality of leadership; the other is incentive factors, that is, consumers perceive employee complaint sources as the best but not necessary factors for enterprises to achieve. For example, employees complain about the lack of promotion opportunities and low sense of achievement. When perceiving employees’ complaints as health factors, consumers’ perception of health factors is the basic factor that enterprises must achieve, which is regarded as the responsibility of enterprises, thus reducing their brand attitude towards enterprises [26] [27] [28] . When employees complain that the source of incentive is the incentive factor, consumers’ perception of incentive factor is the basic factor that enterprises do not have to do, and they will not blame enterprises too much, [29] which is not enough to affect its brand attitude to the enterprise. Based on previous research, Hypothesis 1 is proposed as follows:

H2: Perceived employee complaints moderate the impact of witness front-line service employee complaints on consumer brand attitudes. When perceiving the source of employees’ complaints as a health factor, the higher controllability perceived by front-line service employees, the lower brand attitude of consumers; when perceiving the source of employees’ complaints as an incentive factor, there is no difference in the impact of high or low controllability perceived by front-line service employees on brand attitude of consumers.

Employee complaints reflect how employees are treated by the organization [14] . Morality is the key causal mechanism of third party perception and judgment [30] . How employees are treated by enterprises will lead consumers (as a third party) to judge corporate ethics. When employees complain about health factors, consumers perceive that health factors are the basic factors that enterprises must do but fail to do. They will think that enterprises violate ethical norms, and thus perceive that enterprises are immoral. When the source of employee complaints is the incentive factor, because the consumer perception incentive factor is the complaint caused by the non-basic factors that the enterprise does not have to do but fails to do, it does not violate the ethical norms, so it will not cause the enterprise immoral perception. Consumers’ moral perception of enterprises will affect their brand attitude, satisfaction and repurchase intention of enterprises [31] [32] [33] . Based on previous research, Hypothesis 3 is proposed as follows:

H3: Perception of corporate ethics mediates the impact of witnessing front-line service employees’ complaints on consumers’ brand attitudes. Witness that the higher controllability perceived by front-line service employees, the lower corporate ethics perceived, thus the lower brand attitude. Only when the perceived source of complaints is health factor, the effect of witnessing front-line service staff complaints on perceived corporate ethics is significant. When the perceived source of complaints is incentive factor, there is no difference between the perceived impact of high and low controllability of front-line service staff complaints on perceived corporate ethics.

Based on the goals of this research and other theoretical studies, this study proposed the following structure in Figure 1.

The paper uses Critical Incident Technology (CIT) to conduct exploratory research to analyze how consumers perceive complaints from front-line service employees. The content of the questionnaire is divided into two parts. The first part is a subjective question. Respondents are asked to recall the complaints they see and hear from front-line service employees as consumers. We define the key event as the complaint between front-line service employees that the respondents see or hear in the consumer context from the perspective of consumers. The specific question is: Please recall that in the past year, have you ever seen or heard complaints from front-line employees as consumers in consumer occasions (such as shopping malls, restaurants, etc.)? Please describe this experience in as much detail as possible. Including: 1) When did the incident happen? 2) What consumption situation did the event take place in? 3) What did the employees say? What did you do? 4) Your thoughts and feelings at that time. 5) Will it affect your opinion of the brand? What is the impact? Why? The second part is the basic personal information of the respondents.

A total of 150 samples were collected through questionnaires published on the Internet. 101 of them believed that they had witnessed complaints from the perspective of consumers. That is 67.3% of consumers believed that they had witnessed complaints from front-line service employees. Among them, 63 were women, accounting for 62.3%; 38 were men, accounting for 37.6%, aged 18 - 48 years. According to the Criteria of Critical Incident Law, this study deleted the complaints of front-line service employees that were not witnessed from the perspective of consumers, and eventually got 95 effective critical incidents. Consumer scenarios focus on restaurants, shopping malls and supermarkets. Table 1 shows some typical events.

The rest of the data collection was completed through the online survey platform “Questionnaire Star” and on-site experiments. The experiment uses a situational simulation method consisting of two parts: the first part allows the subject to read the situation carefully and imagines that he is the consumer in the situation. The second part is to let the participants evaluate the perceived controllability, corporate ethics and brand attitude of the perceived employee complaints. The third part allows participants to report basic demographic information and answer their views on the purpose of the experiment. The entire experiment took about 5 minutes. After deleting the questionnaire with too short response time and obvious regularity, a total of 271 valid questionnaires were obtained.

(Chart source: authors sorted according to the content of the questionnaire).

This study includes three core variables: perceived corporate controllability, perceived corporate ethics, and brand attitude. The measurements are derived from or adapted from existing research. Among them, perceived enterprise controllability uses “I think the reason for employee complaints is that the enterprise can control” “I think the enterprise can prevent the reasons for employee complaints” and “I think the enterprise can avoid the reasons for employee complaints” [27] [34] ; Perceive corporate ethics with “dishonest/honest” “insincere/sincere” “swearing/indecent” “untrustworthy/trustworthy” [35] ; Brand attitude with “I have a good impression of the brand” “The brand can attract me” and “I feel positive about the brand” [36] . All variables were measured using the Likert 7-point scale. Among them, 1 means completely disagree, and 7 means complete agreement.

・ Literature review. Collect and sort out the previous research results and research status of important variables such as employee complaints, service contacts, witnessing front-line service employee complaints, perception of corporate ethics, deduce the logical relationship between variables in this paper, build a theoretical model, and preliminarily draw research hypotheses.

・ Critical Event Method. Since no scholars have studied the impact of complaints on consumers before, this paper first uses the critical event method to conduct exploratory research to confirm that complaints do exist among front-line service employees, and consumers can indeed see or hear complaints among front-line service employees, which provides a basis for empirical research.

・ Experimental study. On the basis of the research hypothesis, the hypothesis is verified by experimental method. Through the situation description, the first experiment is the shopping scene in the mall, and the second experiment is the dining scene in the restaurant. The subjects are asked to imagine themselves as consumers in the situation, and then answer the relevant questions.

・ Data analysis. This paper uses SPSS 20.0 statistical software to analyze experimental data. The analysis methods include descriptive statistical analysis, reliability and validity analysis, variance analysis, regression analysis, Bootstrap analysis and so on.

Most of the subjects of the study were female and most were between 21 and 30 years old. Most of the subjects graduated from college. Table 2 shows the analysis of basic information of the respondents.

The results are presented Table 3. All tests achieved significant levels.

The correlation coefficient between perceived enterprise controllability and perceived corporate ethics in Table 4 is −0.261 (p < 0.01), which is significantly negatively correlated; the correlation coefficient between perceived enterprise controllability and brand attitude is −0.276 (p < 0.01), which is significantly negative. Correlation; the correlation coefficient between perceived corporate ethics and brand attitude was 0.376 (p < 0.01), which was significantly positively correlated.

Using one-way ANOVA, when perceiving the source of employees’ complaints as a health factor, we can see that the perception controllability of front-line service employees’ complaints has a significant impact on brand attitude (F(1.66) = 9.69, p = 0.003 < 0.05). The mean difference of perceiving the impact of high controllability of enterprises and low controllability of enterprises on brand attitude is 3.06 and 3.67, respectively. Certificate front-line service employees complain that the higher the perceived controllability of the enterprise, the lower the attitude of consumers to brand. H1 has been verified.

To further test the moderating effect of perceived employee complaint sources on the relationship between witness front-line service employee complaint and brand attitude, a general linear model was used to analyze the results. The results showed that the interaction between perceived enterprise controllability and perceived employee complaint sources was significant (F(1.133) = 3.97, p = 0.048 < 0.05). Simple effect analysis was carried out. When perceived employee complaints are health factors, perceived enterprise controllability which witnessed front-line service employee complaints has a significant impact on consumer brand attitude (F (1.134) = 5.76, P = 0.018 < 0.05). When perceived employee complaints are motivating factors, perceived enterprise controllability which witnesses front-line service employees’ complaints has no significant impact on consumer brand attitude, F < 1. H2 has been verified in Figure 2.

According to the intermediary analysis procedure proposed by Zhao et al. (2010), and referring to the intermediary analysis model (model 8) proposed by Preacher et al. (2007) and Hayes (2013), Bootstrap intermediary variable test was carried out. Perceived corporate ethics mediated the interaction between witnessing front-line service employees’ complaints and perceiving the source of employees’ complaints on brand attitude [29] [37] [38] .

When perceiving the source of employees’ complaints as a health factor, the mediating effect of perceiving corporate ethics is significant. The confidence interval of Bootstrap test is (LLCI = 0.0080, ULCI = 0.289) without 0. When perceiving the source of employees’ complaints as an incentive factor, the mediating effect of perceiving corporate ethics is not significant, and the confidence interval (LLCI = −0.0399, ULCI = 0.659) contains 0. H3 has been verified.

(Chart source: authors sorted according to the content of the questionnaire).

(Chart source: authors sorted according to the content of the questionnaire).

Note: **p < 0.01 (Chart source: authors sorted according to the content of the questionnaire).

First, from the perspective of third-party perception, this paper verifies that the perception of corporate controllability by front-line service employees will significantly affect consumer brand attitude, and the higher the perception of corporate controllability by front-line service employees, the lower the consumer brand attitude. Witnessing complaints from front-line service employees will lead to consumer thinking. When consumers think that complaints from front-line service employees are caused by employees’ dissatisfaction caused by controllable but uncontrollable control of enterprises, consumers will judge it as the responsibility of enterprises and consumers’ brand attitude is lower. That is, how an enterprise treats its employees will significantly affect consumers’ perception of the enterprise.

Secondly, it defines the boundaries of the impact of witnessing the complaints of front-line service employees on consumers’ brand attitudes. Complaints from different sources have different effects on consumers. Only when perceived employee complaints are health factors, witnessing front-line service employees complain that perceived corporate controllability has a significant impact on consumer brand attitude. When perceived employee complaints are incentive factors, there is no difference in the impact of perceived corporate controllability between front-line service employees and consumers’ brand attitude.

Thirdly, by introducing the theory of moral justice, it proves that consumer witnessing the complaints of front-line service employees will cause consumers’ perception of corporate ethics, thus affecting brand attitudes. How employees are treated by enterprises will lead to consumers’ judgment on corporate ethics. In the process of judgment, the greater the responsibility of the organization being investigated, the lower the perception of corporate morality. Only when the organizational behavior violates the ethical norms, can the enterprise be perceived as immoral. Therefore, the higher the perceived controllability of the enterprise, the lower the perceived ethics of the enterprise, and the lower the consumer brand attitude. And only when consumers perceive employees’ complaints as health factors, consumers think that enterprises violate ethical principles or ethical standards; when consumers perceive employees’ complaints as incentives, consumers think that enterprises have not violated ethical standards.

The paper examines the impact of perceived corporate controllability on consumers by consumer witness front-line service employees, and provides important guidance value for the management of front-line service employees and the promotion of sustainable development.

The theory of moral justice is introduced to verify the mediating role of perceived corporate morality. The theory of moral justice emphasizes the important role of morality and provides different ideas for solving management problems in enterprises. Based on the theory of moral justice, this paper verifies that how employees are treated by enterprises will lead to consumers’ judgment of corporate morality, and adds empirical research on the theory of moral justice in management issues.

The moderating effect of perceiving the source of employee complaints was discussed. Complaints caused by different sources of complaints reflect different problems and contradictions, which can affect consumers’ perception of corporate ethics, thus clarifying the boundary of witnessing the impact of complaint behavior of front-line service employees on consumers’ brand attitude.

For enterprises, more attention should be paid to the complaint behavior of front-line service employees in management, such as establishing staff counseling mechanism, increasing psychological counseling to reduce the negative emotions of employees. At the same time, enterprises should do a good job in influencing employees’ job satisfaction, and actively explain to stakeholders the uncontrollable internal management factors in order to alleviate stakeholders’ negative perceptions and subsequent reactions, and further properly publicize employees’ internal responsibilities, so as to promote the brand building and sustainable development of enterprises.

This study has limitations and shortcomings: 1) The purpose of this study is to reveal the impact of witnessing front-line service staff complaints on brand attitudes in consumer situations, so the results may be difficult to extend to the impact of employee complaints in non-consumer situations on enterprises. However, with the development of social networks, media and so on, the number of third parties in non-consumer situations will increase, and there will be no further development. To study the impact of employee complaints on brand attitudes in non-consumer situations. 2) The research background is that front-line service employees complain about the third party (enterprises or other employees, etc.) rather than complain about each other. Whether the research conclusions can be applied to front-line service employees’ mutual complaints remains to be further verified. 3) Using situational descriptive stimulus ignores the impact of complaints from front-line service employees on consumers. 4) The attitude of front-line service employees who complain or their interaction with consumers may have an impact on the results of this study. The relationship between consumers and front-line service employees has not been further verified. 5) Perception of corporate ethics only partially mediates the impact of witnessing front-line service employees’ complaints on consumers’ brand attitudes, while other influencing mechanisms remain to be explored. Step analysis. These deficiencies should be improved and perfected in the follow-up study.

This study only considered the moderating effect of perceived employee complaint sources, but did not further explore that consumers with different characteristics may have different perceptions of complaints. Third parties believe that unfair events can be considered fair by another third party, and vice versa. The interpretation of the enterprise or its agent may also affect the perception of the third party, effectively reducing the impact on the brand. In future research, we can consider such moderating variables as increasing the relationship between consumers and employees, consumers’ moral identity, and consumers’ public self-awareness.