That is an easy question for me!
Nothing - because I have never sold one, so I don't know.
I have started a graph with prices that people have sold their cars for or purchased them for. It is amazing, but there is a nice curve to the graph and I can just about figure out any car and what the average price would be. I would then set the price on the high side.
I am going to post this graph when I get it set up a little better.