Building a site like mixed with features from http://screencast.com/t/vIAc9lxTJIr and http://screencast.com/t/2WmTC8MOl The number of products displayed can dynamically change http://screencast.com/t/HuqqCFamAs It will be a feature by feature match of those two sites. There will be an auction system like http://screencast.com/t/LIvUaI7myj with a stores feature for the sellers. The credit card info will be automatically charged using http://screencast.com/t/gPMPvR1di The best bidders will have tons of Ecommerce experience, the ability to handle such complex features, and great feedback. You also have to convince me that the cart you plan on using is the best cart to use, and why..