Most of the security proposals in commerce scenarios have been based on a classical e-payment system definition. This definition basically represents a client who sends a payment order to obtain some goods/services from the merchant, which the intentions of the real money transaction carry on between his financial institutions. Nevertheless, these definitions are not sufficiently robust when new aspects appear in the electronic payment transaction. We can identify some of those new aspects (such as: smart card with network capabilities, business mediator with advantage services, handheld devices with constrained connectivity, and multiparty scenarios) that could subordinate the design of current and future commerce scenarios. In this paper we extended the traditional e-payment system definition, in order to include these new aspects. Additionally, we describe two new payment models, where such aspects are involved, and where the secure solution needs to consider new security requirements.