I've always done Pre-Purcahse Inspections at shops. They caost around $200 but it's cheap ionsurance to know what you're getting into. Almost bought a 2003 540i last year and after running the PPI I found out the car was a "lemon" and was going to need $5,000 in parts & repair over the next year. Ran away from that thing fast! Definitely worth the $200.
'91 M42 E30 - All sorts of goodies.