In the increasingly competitive service industry, organizations require frontline employees to deliver customer service while simultaneously driving sales to enhance overall performance. However, employees face significant challenges in balancing these dual tasks. Grounded in social exchange theory, this study adopts a cross-level analysis to examine how group-level self-sacrificial leadership fosters employees' service-sales ambidextrous behavior through leader-member exchange (LMX), harmonious passion and shared vision. Employing structural equation modeling on data collected from 312 employees and their leaders across 20 companies, the findings reveal that self-sacrificial leadership directly promotes service-sales ambidextrous behavior and exerts an indirect influence through LMX and harmonious passion. Moreover, a shared vision within groups significantly enhances the positive effects of LMX and harmonious passion on employees' ambidextrous behavior. These findings highlight key mechanisms underlying the development of service-sales ambidextrous behavior and offer practical insights for organizations to foster flexibility and improve performance in dynamic and high-pressure environments.