All bids made in the Real Estate and eBay Motors vehicles categories are considered non-binding.
You should take lots of pics and be honest about the car. But the buyer can show up to look at the car and say "no thanks," or not show up and just change their mind.
Still, it might not be a bad way to get a lot of eyes on your listings. Don't take paypal or credit cards through paypal, or the buyer can get the payment reversed after they take the car.
I sold my last 5 cars on ebay. What is nice is you get market value and the car is usually sold in a week. The fees are reasonable.
Have lots of well-lit pictures, I set my camera to fill in flash on overcast day for best results. Open all the doors and sunroof to let light in for the interior photos. Show all defects.
Disclose all defects. Accurately describe the car's condition -- there should be no surprises for the buyer.
Start the bidding low. Unless you absolutely cannot afford or stomach it: use a no-reserve auction.
A car should not be the first thing you sell on ebay. Have a feedback score built up and a good Seller Reputation before you list a big-ticket item like a car.
I never realized the bids were non-binding. All my sales went through without a hitch.