I found my car on eBay. I did't buy it through eBay though.
Anyways, when looking for cars I found that lots of pictures are a must. When people are looking at cars knowing what they are buying, especially such a valuable item, is important. I would note and photograph all major flaws. Also in your description I would be as detailed as possible, and as honest as possible. Make sure you are as acurate as possible too. In some descriptions of cars with lots of !!! and CAPS makes it seem like they are really pushing the car upon you. Going above and beyond saying how amazing the car I find is very "pushy", though it is important to say good things about the car, as long as they make sense. I read a description for a Land Rover Discovery that said it had amazing acceleration and handling- yea 0-60 in 11.2 is "amazing".
I dunno, those are just some points that I would like to see when buying a car online.