[hytem]

Ebay is an imperfect setup with no guarantees. Some of the bidders are phoney, and some of the sellers are phoney. Watch out for Rolex watches. Pay with paypal--they cover fraud for up to a $1000. And there are tons of gray art for sale by famous names--some of it probably real but difficult to authenticate.
For cars, ebay is a good starting point for what's selling in your area. If you like one, contact the seller, see the car and maybe he'll take it off ebay if you can agree on a price. A lot of cars get sold that way on ebay--maybe a majority.