I'd just move on and find another car. A corporations attorney will outlast your own pocket book. It's not even worth it. Come to some agreement. They actually do have every right to sue you if you came in between their contract. eBay is not a binding contract. Period. Imagine all the buyers that back out? You can't force them to pay. Vice versa. Sadly glitches do happen.
Current Stable: Some Audi with a V10, Couple of BMW's, one F Car, and one P car. One lonely GT-R with all the Euros.