So here's my dilemma now...
Do you like the car?
Is the price/mileage reasonable for this car?
Did the car get a clean bill of health from the mechanic (meaning no problems that need fixing and the mechanic has no "warnings" about this particular vehicle)?
Do you have reason to believe the owner mistreated the vehicle?
If you are happy with all the answers to these questions, then buy the car. Just accept the fact that, as a rule, maintenance on this vehicle will be more costly because it's a BMW. Keep up on your routine maintenance and repairs like you should and see how far you go.
Life is full of "what if's", especially with used cars. But in the end, all you can do is make a reasonable approach to the vehicle and either go for it or not.
BMW does NOT, as a rule, make crap cars. They have a well earned reputation. So if the car is in good condition, not been abused, reasonable miles on it with a reasonable price...go for it.