Another reason for not competing with eBay is that those who list timeshares seek the widest audience possible, hoping that someone who is not knowledgeable about the resale market will bid up the price. They get that wide audience on eBay. Since TUGgers are more knowledgeable, a TUG auction might well generate a lower price than eBay; certainly no higher than eBay.
At the same time we know the way things should work, know about escrow and how things can get hung up. It might make for a smoother transaction as opposed to the way one may go on eBay. If I were selling, I may very well be willing to take less money for a smooth transaction. Also, I imagine we'd get very few inquiries from Postcard Companies on listings here (at least compared to what one might get as a result of an eBay transcation).
Most of us know that an eBay auction for a TS is really an expression of interest in said TS and not binding; the "higher" price may fall through. I imagine any sort of auction here would also be non-binding.
Logistically, would it only be available to Members?
Of course, there is already a place for Members to sell their TS right here on TUG, so the idea may be moot anyway. Price it right and it'll sell.