P2P applications support exchanging resources while preserving total or partial anonymity of both requestors and providers. However, concerns have been raised about the possibility that anonymity may encourage malicious peers to spread tampered-with resources (e.g., malicious programs and viruses). A considerable amount of research is now being carried out on the development of trust and reputation models in P2P networks. In this paper, we assess the efficiency of our approach to the design of reputation systems involving flexible techniques for collecting and aggregating peers? opinions via comparison with probabilistic approaches.