Make him pay more and hope he either really wants it or get's stuck with it.
Done that meownself but I like to think they get stuck with it.
Usually if its something I really want it goes out of sight. If I don't really care it goes cheap. I watched a buttload of Single Six cylinders go for 40-50 bucks but the ones I bid on went a lot higher. I finally got one but I paid 80 some odd dollars for it.