You bring the car to a QUALIFIED BMW mechanic, have them inspect the car for any damage, defects, repairs...include a dump of DME data (engine computer) and look for any old codes, evidence of 'over-revs;, etc

You do this BEFORE you buy.

You DO NOT believe the selling dealer when they say "our mechanics went through this with a fine tooth comb"... personally I don't even accept a BMW dealer and a CPO! Many people have bought CPOs only to find the car has damage, defects and issues, and BMW will not stand behind it.

Carfax and the other databases are fine for info, but only a fool will rely on them.