I'm quite surprised at the responses so far.
My Z4 Coupe had 1 previous owner when I bought it at 1.5 years old. That didn't put me off. If I sold it now, with 2 previous owners, at 2 years old, I still wouldn't expect people to be put off. Now, if he had said 5+ previous owners, I'd perhaps look into it a bit more, but as mmm-five has said, in the current climate, it's not exactly rare.
Regarding price; I don't feel it's a rip-off by any stretch, but it's not the best price out there. You most certainly would NOT be getting an M for that price. Bear in mind he wants the Coupe, which commands a premium over a roadster, regardless of what roadster owners will tell you.
As an example though Adam; my car (in my signature) went up for sale recently at £19,500, and I expected to get £19,000 for it. Mine is an August 07 car, so most likely almost a year newer than the one you're looking at buying.
I hope that goes some way to helping you Adam, but please feel free to ask any more questions. Everyone on here is very helpful.