Purpose: The old axion to put the customers first (e.g., customers are king, customers are always right) has been taken for granted in the service sector. In addition, many companies in South Korea are providing customer-first education for employees at their contact points to strengthen their competitiveness. However, excessive increase in the psychological power of the customer can lead to a problem of abuse of power, called 'Gap-jil.' Despite these concerns, most companies hardly discard policies to give high priority to customers because of the assumption that it enhances customer satisfaction leading to organizational performance. However, in recent years, some franchise catering companies have posted warnings about the abuse of power by customers, and a movement to pursue a power-balancing between service providers and their customers is spreading. Research design, data, and methodology: This research is conducted to reconsider the principle of the customer-first perspective and to create a basis for arguments that can solve the problem of abuse of power, which is recognized as a serious social problem. In this research, we test and analyze the effect of customers' psychological power in the context of a restaurant on expectation for service and response to service failure. Result: The result of an experimental study shows that the effect of psychological power on customer satisfaction can be somewhat negative. Also, customers with high psychological power are more likely to have high service expectations. Especially high psychological power of customers causes a difference in the expectation level of human factors such as employee attitude, while the difference in expectations of non-human factors such as restaurant atmosphere was not statistically significant. In addition, when customers with high psychological power encounter service failure situation, they are more likely to feel disappointment and regret with a service provider. Meanwhile, the effect of psychological power on complaining behaviors are not significant. Conclusions: The findings of this research provide meaningful implications that the service providers should reconsider their existing corporate culture and management policies that put customers first. In addition, the result of this research is provided meaningful opportunities to review the management philosophy for the company's customers and the education philosophy for the employee education.