it seems like, you took 2000 from him after negotiating on a price. And later on when someone else saw the car and offered you more, you sold to him (The guy offering more).
If this is the case, then goodluck man, you should receive calls from him. This is unfair from your side!
If his behavior was erratic, as you mentioned, then why you made the deal and took 2000?
sorry mate, you are confusing!