In distributed systems, traders mediate between clients and service providers. This paper introduces a trading model, which supports multiagent systems (MAS) and goes beyond simple trading in three ways: (a) Service composition -The trader composes complex services of the current service offers. During the composition, it checks the availability of the service offers. (b) Use of group agents -Group agents represent a group of agents with their individual policies and other context information. The trader can use the group agent's information for a pre-selection of service offers. (c) Adaptability -The trading model uses the notion of clients' trust into services and adapts to the clients' preferences and system policies. The trading model is used in a Computer-Supported Cooperative Work (CSCW) application, in which the trader finds adequate communication services for project teams with geographically distributed members.