From the buyer's perspective, make sure you take some damn good photos after having the car detailed. Bad pictures can make or break a sale.
I've purchased two cars from eBay, not a single problem (except the bitch took the CD player out of one of the cars, but said in the auction it came with it). Bought them for 50% of the retail value. Had to fly my dad about 700 miles away to get it but he didn't care, free trip.
He also purchased a 77 Trans Am off eBay and got hosed.....big time. Turns out the car was TWO car welded together. Since he bought it in Florida, it was shit out of luck. I guess you can sue people there, win, and they don't HAVE to pay (or so says his GM lawyers). He took a big hit to the tune of $12k. Thankfully a flood ruined the car and he got that and then some back.....very lucky man.
But really, just make sure you use your head and post the auction like you would want to see as a buyer.