I bought my car(E30 M3 Cab) from Independent Motor Company near Reading. Basically, don't go there - let's just say they've had some problems with Trading Standards (phone Reading or Windsor Trading Standards). My car turned out OK but was totally miss-represented. You can't trust a word the salesman says so get any car checked by a genuine M3 expert. The cheap RAC inspection Independent does on the cars isn't enough. They probably won't have even rectified any faults the RAC inspection found anyway. I agree with Phil about Birds. I always get my car serviced there and they are excellent. Even if you don't buy an M3 from Birds I'd strongly recommend getting it serviced there.