This depends on both a large density of users and readily available merchandise (e.g. a warehouse). Of course, in my experience, the only reason people go to eB

This depends on both a large density of users and readily available merchandise (e.g. a warehouse). Of course, in my experience, the only reason people go to eBay is for things they can't get on Amazon - collectibles, used clothing, items not manufactured anymore. None of these combine well with warehouses due to their relatively unique nature.