Building an agent-based network of service providers and requestors requires the effective management of the interactions among peers. These interactions, as in real life, require the mutual trust of the peers participating in a negotiation process. Trust quantification is a complex process that involves many parameters. Applying trust mechanisms in a P2P network is essential for guarantee the trustworthiness of participating peers and eventually the success of the negotiation. In this paper, we propose an agent-based community-centric P2P organization of service providers, clients and intermediaries that effectively and securely collaborate with each other, by considering common context in their negotiations, to discover trustworthy request-relevant services. The paper defines the formalisms for: 1) the roles of peers, and 2) the trust model which considers peers? reputation and secure message exchanges.