In the UK there is an essential service at 1200 miles to change from 'run-in' lubes and (I believe) tighten down head etc. Any car which hasn't had this done by 1800 miles is considered very dodgy and for good reason (so warranty issue).
Many such cars come up for sale at attractive prices, because without that magic stamp in the book the value is much less. There is a market for faked service schedules, so always check with the dealer whose stamp is shown. If possible I'd go back to first owner (and others if possible) to check how they treated it.
Oddly, despite their electronic wizardry, BMW do not seem to have any way of telling if the car was broken in gently. I wouldn't worry too much, as the racing boys tend to ignore this, driving like 'sh1t' from the word go. It is supposed to give an extra 5-10 bhp (or PS?) but may well mean more oil is burned, though this 10% thing (above) sounds pessimistic. I treated mine like royalty and I burn no noticeable oil - she runs like a Singer showing machine with masses of power when I get on the treadle.
Good luck with a wonderful (if 'interesting') car! And get SMG if possible (see separate thread)!