At the risk of offending, I am going to suggest you search around here a bit and educate yourself on buying an M. Not just this particular issue, but many folks (myself included) have posted about issues that come up during the acquisition phase. By reading what others have found you will save a lot of time and (potential) heart ache.
There are numerous, numerous posts on rip off and pit falls with dealer, on line sales, etc, etc. Autotrader is pretty good- yahoo cars is the worse.
Cheap M5's - what gives????
Yet another scam
Too Good To Be True?
Check this scam out!
FYI- I am a pretty vocal 'cheer leader' for folks looking to get 'on board' - don't take this the wrong way- there is just so much info here on everything about buying a car it is a shame not to take advantage of it!
Good luck
A