This article sheds light on the restrictive and/or enabling dimension of the socio-technical devices implemented by peer-to-peer access platforms. The authors carried out a cross-comparative study of the interactions initiated through the Mutum and OuiCar platforms. They show how the constraint exerted by platforms is not applied mechanically, but dynamically arises from the interactions between users in more or less free moments. In triadic relationships (provider, obtainer, intermediary), the constraint is therefore relative and can be understood only by studying the different moments of interaction and practice, beyond the frame established by the platform.