+1,000,000 to what everyone has said.
And a contract doesn't guarantee he'll sell you the car, it just means if he doesn't can sue him for breach of contract.
There are too many M3s for sale that you don't need to mess with this.
2012 Ford Raptor (weekend toy)
2011 AW E90 (current)
2007 MB ML63 (sold)
2006 Porsche 911 C2S (sold)