First off I personally ebay very little. It is time consuming vs alternatives. I mostly craigslist them then set them aside until they sell. As far as criteria AFTERMARKET (not a galvanized tin box) 400+ Watts and SATA. Also...most of the keeps end up going into cases I get that are aftermarket and I use it as part of a build...reuse. 400 will run dual some quad cores and on board graphics, OR 75W quad core and a single graphics card...your sort of limited with that so selling them is...a shot in the dark I'd say.