This study seeks to investigate the effect of internal marketing—treating employees as internal customers—on salesperson's engagement in customer‐oriented behaviors and resultant customers’ responses. The data were collected from dyadic interactions between salespeople and customers in banking firms in Vietnam. The results showed that internal marketing is significantly associated with salesperson's performance of adaptive selling behavior, customer‐oriented selling behavior, and relational selling behavior, which result in customer relationship continuity, purchase intention, and positive word‐of‐mouth. In addition, salesperson's customer‐oriented behaviors play partial mediating roles between internal marketing and external customer responses. The study extends the extant literature of internal marketing and offers useful managerial implications for service firms, particularly banking firms in Vietnam. The study concludes with suggestions of potential research directions for future studies.