1. It's going to be almost impossible to get a guarantee on a used, heavily modified vehicle. Even if he wrote one up, it wouldn't be guaranteed that a judge would accept it if you had to take him to court.
2. Even if you could get a guarantee, you are still overpaying by a lot for a car like that. It is not worth $4500.
2. Even if you could get a guarantee, you are still overpaying by a lot for a car like that. It is not worth $4500.