You should research timing chain issues with the N20 engine in the X3 28i. If the timing chain guides fail during operation you may be looking at a bill for a new or rebuilt engine which may range up to $20,000. Maintenance costs from a BMW dealer or even some independents should be investigated.
A couple links to threads for your consideration follow:
http://x3.xbimmers.com/forums/showth...t=timing+chain
http://www.bimmerfest.com/forums/sho...d.php?t=922040
http://www.bimmerfest.com/forums/sho...d.php?t=912547
Some questions to consider:
Has the timing chain been serviced and the timing chain guide replaced with the improved part introduced in 2015?
When were the brakes last serviced?
Are suspension and cooling system components original? If so they are likely to need replacement soon.
Was maintenance done to the old school standard some recommend for BMWs to remain reliable beyond 100,000 miles? Use a search engine to find Mike Miller's Old School BMW Maintenance Schedule (e.g. v02.11) and read it carefully.
Do you know if a previous owner used a chip to boost engine output?
Do you know if the engine was broken in properly by the first owner?
Will you handle service yourself? If not, are you prepared to pay a bill of >$1000 each for problems related to turbocharger, coolant system, electrical, steering, suspension, brakes, drivetrain, etc. when these arise?