If anything that should be a good sign that at least he checks the oil and is on top of it , most people dont even check the oil level and just wait till they hear a knocking sound comming from the engine bay to realize that they ran it low.
I havnt talked to the owner so i could be wrong but that car seems to have over 140k miles and it would be 100% normal for it to burn oil at this point.
As for the price i dont see anything fishy about it , the car is not in the best cosmetic condition and it probably has high miles so the price sounds about right . This is just a car that you have to go over with a fine tooth comb before you get it but could be a good bargain for the right person .

Anyways GLWS !! And great price on a e36 m3 !