We present TrustDavis, an online reputation system that provides insurance against trade fraud by leveraging existing relationships between players, such as the ones present in social networks. Using TrustDavis and a simple strategy, an honest player can set an upper bound on the losses caused by any malicious collusion of players. In addition, TrustDavis incents participants to accurately rate each other, resists participants? pseudonym changes, and is inherently distributed.