No matter what type of car you are interested in and especially when looking for a BMW you should always try to buy the best (usually the more epensive) example of the particular car you want. You will pay more up front for a better condition car or pay more later fixing a car that isn't so good, but seemed like a good deal initially; you will always pay one way or the other...
It almost always costs more money and definatly more in bullshit in the end to correct/fix that "good deal".
You really don't know what was damaged, since you didn't see the damage and the current owner isnt going to tell you the real story so take some time, save up some more money and find one that hasnt been wrecked. You will be glad you did.
These cars do not suffer fools very well and they can empty your pocket very rapidly.