There are a lot of research problems behind constructing a good search results page. This includes what items to show (recall), in what order to show them (ranking), how to detect users who are gaming our system (spam), what to show in the left-hand control panel (search suggestions). I'll mention two examples to give the flavor of the problems. Some sellers game the system with shill buying rings: they have shills purchase their items to get artificially high feedback. Detecting this is challenging. Second example is ranking. In web search, results are ranked by relevance. But in eBay we have to balance relevance with value. The item that is most relevant to a query could be from a seller with bad feedback, or at an unreasonable price. How should that be ranked compared to an item that is slightly less relevant, but has better value?