What the auction is likely saying is that they are M3 style
rims as far as the look, but not the actual rims found on a stock M3. I doubt very much that you could fit those rear wheels without rubbing or rolling the fenders, and the offset is probably incorrect. The largest typical width for an E46 in the rear is 255 w/o modifications. 19" is a lot of unspring weight for the suspension, and you'll suffer more drivability issues than any benefits you may gain in my opinion. For E36/46 wheels, 17" seems to be the magic number.