I think most people enjoy the ebay threads. I don't browse ebay myself, so it's interesting to see what goes up for sale there.
What some forums do is dedicate a thread to something like ebay auctions, sticky it and only allow auctions to be posted there. That might be a solution, but it requires fairly diligent moderating to make it work. No disrespect to Philip, Cindy, Anita, et al - who I know all have busy lives - but unfortunately, one of the long-standing criticisms of MC is that it's very loosely moderated and because of that I'm not sure if a solution like that for ebay auctions would work here.