The integration of robots in customer service has attracted considerable interest from both academia and industry. While some studies highlight positive impacts on customer experience, others report neutral or negative outcomes. This meta-analysis synthesises findings from 25 articles comprising 62 independent studies, 147 effect sizes, and a cumulative sample of 19,668 participants. The results indicate that robot-provided services generally reduce customers' positive emotion and intention compared to human-provided services. However, upon closer scrutiny, we found that robots outperform humans in contexts involving embarrassment (vs. non-embarrassment) and in services with a utilitarian (vs. hedonic) orientation. Fur, robot use is more effective in low (vs. high) complexity service settings. Furthermore, humanoid robots with visual output capabilities are more effective than non-humanoid or text-based robots. Moreover, the negative effects of robots (vs. humans) on customers' satisfaction and intention are less pronounced in product-oriented industries or sectors like electronics and retail than in service-oriented ones like healthcare and hospitality. These findings underscore the conditions under which robots are suitable for customer service, thereby providing valuable insights for strategically optimizing their deployment to improve customer experience.