I respectfully disagree with the above, bidding will get you the best price in my opinion. Buy it now works sometimes in addition to auction format, but its not the best strategy on its own.
The more "risk" you show you're willing to take with your final price, the more excited people will be about bidding on your item. An item with no reserve always gets more bids than one with. A "buy it now price" really just advertises what you want for the car, so a reserve with a buy it now is basically telling the bidder "take it or leave it, here's the price." That defeats the purpose of an auction site, which can be used to your advantage as a seller.
The strategy is that bids generate more bids. If your car moves up to 2000 dollars for a selling price with 20 bids, its much more likely to tack on another 500 bucks in the final few hours than if it had moved up to that price with 1 or 2 bids, or it had started there, especially, as I mentioned above, if there's no reserve on the auction.
Set your opening bid at 10% of what you actually want for the car. 500 dollars for a 5000 dollar car, etc. The first guy is going to bid within hours to a day or two of the auction opening because everybody has that hope that they'll get something for nothing. The next guy will do him one better, and so on: the frog-on-a-hotplate theory. By the end you've probably generated a price that moves the car from "deal of the century" to "a relatively fair price" but you won't keep bids going unless you have other bids to drive some excitement.
Also, I would say spend the extra 15 cents, 25 cents, 1 dollar here and there on your ad to make it look decent. The little flag icons and such are useless, but a highlighted ad will do you wonders. The more pictures, the better. I have no idea how people expect to get a good price on a car with 3 blurry pictures. Take your car and wash it, get some clear coat and degreaser and do up the engine bay, why not? 10 dollars and an hour's worth of effort will generate has generated me 25% better selling prices than comparable vehicles on ebay (we can be talking thousands in some cases). Don't be lazy, take the time.
Last, the description matters. Highlight the good things but be honest about problems. I usually write at least two or three large paragraphs detailing the history of the car, how I've treated it and how its served me in addition to the problems and highlights of the car.
A lot of it is common sense. Take a look at a couple pros on ebay and see how they make money. People are throwing cash at them for cars just because they talk them up and make them look nice by taking quality pictures. Anybody else can do the same-
K