I don't know the seller either, but why does it matter what car the wheels are from? As long as the wheels fit, or don't fit, your car, that's the most important point, right? As far as hub centric rings, if you need 74.1 mm rings, just buy a set for $4 ea from BBS USA.
Just thinking aloud here, but what if the seller bought them used for his car, but they don't fit and he never took pics of them on his car. In this case, he won't know what car the wheels were originally on.
Another scenario: the seller found them for a great deal somewhere and is trying to flip them for a profit. That's not illegal either, right? He also won't know what car they were originally from.
I like the wheels too but I think $2k is too rich for my blood at this point. They'll fit great on both my E39 wagon and E38.....