Go the guys house with a truck and trailer and get that car. If not, threaten with your lawyer. That is about all you can do. This happened to me just months ago and I was unsuccessful in getting the car. I have half the money back and working on the other half. What a shame. This is a negative side of the hobby! Crooks.
edit... if you have a signed contract and he neglects to fulfill his end of the contract than he is in violation of specific performance. Call you laywer!