Summary form only given. One of the underlying assumptions on the design of peer-to-peer (P2P) network is that each peer trusts each other for forwarding transit messages. However, with the growth of P2P application, especially in business model, some peers may behave as selfish, irrational nodes due to conflict of interest or for conservation bandwidth. In our model, the P2P network is considered as a virtual market place where peers can find, provide, and use services. Since peers are owned and operated by different entities, they do not necessarily share the same goals, but rather, to serve their own interests. In this paper, incentive mechanism to motivate peers to forward transit messages is proposed. We have implemented the monetary/token as an incentive mechanism, in which peers can setup their cost to charge for transiting a message. We also show that a peer may setup transiting cost higher or lower than other peers, but the strategy on setup the cost reflects its benefit.