Deigueiredo and Barr have an interesting paper TrustDavis: A Non-Exploitable Online Reputation System. In their paper they discuss the problem of identity. I propose to avoid the problem by using a developing trust signature sort of similar to the web-of-trust (explanation and analysis) or Friend-of-a-Friend but constructed using an individual's online behaviour (see Goldbeck's paper on Semantic Web Interaction through Trust Network Recommender Systems)