[vafan13]

a good exclusionary warranty is worth it *if* you can find one for a not-ridiculous price. That seems to be hard these days. That said, the car is pretty reliable, just need to treat it right.

how much oil consumption is he getting? Less of a problem with 14s on, but good to ask.

check to make sure the AC gets cold. AC compressors are known to fail on F10s in general.

how do the rotors seem? Rotors for these babies are not cheap. Might as well ask about/check pads, too.

is it smooth on a cold start?

other than that, fluid leaks are what I'd be looking for. this thing has hoses coming out of hoses coming out of hoses. Unfortunately, with that bottom splitter trey and reinforcement plate, there's a good chance one wont just see fluids on the floor, though one might be able to see residue from evaporated coolant or oil splatter.

Personally I'd just pay to get a PPI done by a reputable shop that knows M cars (or at least BMWs).