We tried that when we purchased, didn't work...
He's a a very small business, and thus doesn't have much overhead. This means if a car doesn't sell, that's ok. It'll sit there forever until it does- he doesn't bring in new cars until the current ones move. Plus, he doesn't do his own financing- just outsources it, so he ultimately gets full payment on each car up front anyway... I don't know, we didn't have enough in cash to really push things our way- but you might. He'll probably hold fast, but it definitely can't hurt to try!