The sharing economy has emerged as an influential research area in which a platform mediates customers’ temporary access to service provider resources. To provide a generalizable picture of the platform's customer and service provider relationship formation process, we integrate effect sizes from 192 studies, including 214 independent samples (N = 88,154). The findings indicate there are motivators and inhibitors for individuals to join a platform as a customer or service provider and that these influence attitudinal and behavioral responses toward the platform through a two-level relationship quality pathway. Moderator analysis reveals that the impact of customer motivators and inhibitors on customer response to service providers and platforms depends on country-level moderators and cultural context. These results provide insight into relationship formation among actors in the sharing economy. The study also makes recommendations for platform managers, especially in hospitality and tourism, to more effectively manage their relationships with their users.