As a frequent buyer and seller on eBay, I agree with C.T. on this one. If I'm the buyer and I trusted a seller enough to send them money to purchases an item in the first place, why should they be any less trustworthy to return my money if I send them back the merchandise? Even if their definition of "mint" doesn't agree with mine? Especially since I can still post negative feedback if they don't return my money.

If I'm the seller, once I receive payment for something and ship it, I post positive feedback for the buyer. If he receives the item and isn't happy, and I send a refund and he doesn't send me back the merchandise, I can't change the feedback rating I gave him. So he would have gotten my merchandise for free and a positive feedback to boot!