Micro-payment systems have the potential to provide non-intrusive, high-volume and low-cost pay-as-you-use services for a wide variety of web-based applications. We proposed a new model, P2P-NetPay, a micro-payment protocol characterized by off-line processing, suitable for peer-to-peer network service charging. P2P micro-payment systems must provide a secure, highly efficient, flexible, usable and reliable environment, the key issues in P2P micro-payment systems development. Therefore, in order to assist in the design of an efficient micro-payment model suitable for P2P networks, we compare and contrast several existing P2P micro-payment models in this paper and outline a new P2P micro-payment scheme we have been developing that addresses the disadvantages in current schemes.