I have never given a deposit on a private sale, not sure I would be comfortable with that.
Can you sell cars to Pick N Pull? I thought their inventory came from Kidney Foundation, I could be wrong...yep I was.
http://www.picknpull.com/we_buy_cars.aspx
Test drive, haggle, have my final offer bluff called, and I leave, call back the next day and prepare to accept their final price, only to find out that the car was sold...happens to me all the time.