This paper deals with the sign up issue in social networks populated with Web services. These social networks can be used for example, to ease the discoveryof Web services. Based on Web services’ functionalities three social networks are built: competition, substitution, and collaboration. In competition and substitution social networks, Web services offer homogeneous functionalities. In the collaboration social network, Web services that offer heterogeneous functionalities. In this latter type, Web services can be put together to develop composite services. Prior to joininga social network, a Web service through a third-party,named social Web service, should evaluate the pros andcons of being member in this network. A set of qualitycriteria for assessing these pros and cons are proposed.These criteria include, but are not limited to, privacy,trust, fairness, and traceability. Policies for managingthe sign up are, also, provided in this paper. The adoption and efficiency of these policies are monitored andassessed with respect to the values that these criteriatake. In response to this sign up’s outcomes, these policies are fine-tuned.