As the number and diversity of electronic commerce participants grows, the complexity of purchasing from a vast and dynamic array of goods and services needs to be hidden from the end user. Putting the complexity into the commerce system instead means providing flexible middleware for enabling commerce within different commercial communities. In this paper, we present one such commerce middleware component --- an Auction Manager designed to simplify and automate both the creation of new markets and the matching of users to existing markets. The Auction Manager determines which markets are appropriate for a given buyer or seller using market-specific inference rules applied to the current market offerings. We also show how these same inference rules can be used by the Auction Manager to automatically compose and decompose market offerings to respond to changing conditions within the marketplace. Finally, we describe how the Auction Manager provides a focal point for expressing policy de..