Depends on your personal levels of risk aversion... BMW dealers are good and offer gold plated warranties. They charge accordingly but still offer value if you're nervous about something falling off. BMW service history is vital if buying privately.
There's plenty for sale so establishing the price for a bare bones bike is easy. Many have been blinged to within an inch of their life and their sellers will want to charge more to cover the costs. Stuff worth paying for IMHO include heated grips, ally panniers. ABS is a contentious issue especially on earlier 1200's.
Good luck - they're a great bike especially if you are going to travel/tour.