Geeze. The worst I ever had was a case of "buyer's remorse" from someone who bought one of my old 1084 monitors off me. The auction closed at 9:30pm on a Friday night and their payment came through an hour or so later (in other words, very late at night). The UPS guy picked up the package on Monday. In my auction I promised "ships within 24 hours", and they tried to go back and say I hadn't done that, in order to get a refund. But obviously UPS Ground doesn't pick up on weekends, so ebay/paypal backed me up, and I got the money. Still took a couple weeks though, and was kind of an unnecessary pain in the ass. I've now changed my auctions to say something like "ships within 1 business day". Jackasses.
But still - never go outside of ebay policies!