That car brand new can be had for $57k. Most cars (including BMWs) depreciate 20 percent when you drive them off the showroom floor.
$49k is 15% off of $57k. So in my mind it is still overpriced. I'll be it doesn't bring $46k. Not only that, it has an unknown history. Why is it for sale after only 850 miles? Maybe the diff fell out for no reason. I would run from that car like it had contageous herpes (maybe it does).