...I think I'll start listing stuff on ebay with that disclaimer....

or perhaps "Please accept my deepest apologies if I decide to sell this item from under you, I'll save a bit on sellers fees, and, well...you probably really didn't need it anyway, or can find it somewhere else.

I'm not involved in any way, but I can tell you I would certainly be less likely to bid on an item with that bit on the listing. Probably Ebay would be less than enthusiastic about it either.