Purpose This study aims to examine how customers derive satisfaction and affective commitment from their participation in financial services, which is conditional on their relationship length. Design/methodology/approach Student interviewers approached customers who were exiting banks at two skip intervals in Taiwan. The final survey sample consists of 227 respondents. Findings Empirical results confirm that optimal customer participation (CP) influences affective commitment through increased customer satisfaction. The optimal level of CP with customer satisfaction and affective commitment is high if the relationship length is long. Originality/value This article shows that the marginal benefits of CP on customer satisfaction and affective commitment become negative after an optimum level. Furthermore, relationship length moderates the aforementioned relationships.