This study analyzed the impact of information about others' willingness to pay on individuals' willingness-to-pay estimates. From an economic rationality perspective, an individual's willingness to pay should maintain consistency and should not be influenced by others' willingness to pay. Even if others' willingness to pay does exert an influence, it can be viewed as conveying information about product quality or value under incomplete information, in which case it can be interpreted within the framework of economic rationality. However, phenomena that threaten the concept of economic rationality have been reported, including preference anomalies such as the willingness-to-pay/willingness-to-accept gap and preference reversal, as well as cognitive bias phenomena such as anchoring. Against this background, the present study addresses the following three issues. First, the influence of information about others' willingness to pay may arise through a low-elaborative System 1 process rather than the high-elaborative System 2 process assumed by the economic rationality perspective. Second, information about others' willingness to pay may function as a social standard against which individuals compare and evaluate their own responses, and this phenomenon may arise from individuals' expectations to be socially accepted and to belong. In this case, others' willingness to pay should be interpreted as serving as social pressure rather than functioning as information. Third, we address the type of information conveyed by others' willingness to pay. One hypothesis is that it conveys information related to others' preferences or social costs, which differs from the product information assumed by the economic rationality perspective. These issues have important theoretical and practical implications regarding the stability of preferences. If the influence of others' willingness to pay follows a System 1 process, this implies that willingness to pay can be influenced by various situational factors. Moreover, if it conveys social information rather than product information, this implies that willingness to pay is influenced by social factors and exhibits instability. To examine these issues, two experiments were conducted in this study. In the first experiment, information about others' willingness to pay was presented after participants completed their initial willingness-to-pay estimates, and in the second experiment, information about others' willingness to pay was presented during the initial estimation situation. In each situation, individuals' willingness to pay, explanatory variables for willingness to pay, and perceived levels of uncertainty regarding estimates were compared and analyzed. The results showed that when high willingness to pay from others was presented, individuals' willingness to pay increased. Additionally, the phenomenon of simultaneous changes in explanatory variables for willingness to pay was observed during this process, suggesting that this process follows the elaborative System 2 procedure. Furthermore, others' willingness to pay was found to convey social information reflecting others' preferences or social costs, rather than product information. This result can be interpreted as meaning that individuals' willingness to pay is not independent of social factors and is unstable. Meanwhile, this study also analyzed the effect of others' willingness to pay on individuals' perceived uncertainty regarding their estimates. The results showed that participants who had perceived higher uncertainty before the presentation of others' willingness-to-pay information exhibited greater changes in both willingness to pay and uncertainty levels. Additionally, the influence of others' willingness to pay was found to differ depending on whether participants had estimated their willingness to pay before receiving the information.