The magazine was suspicious. Don't know if the OP was hoping for a collectable, or a shooter. Certainly looked like a nice shooter. I would question it being all original.
The magazine was definitely not period correct, being aluminum; 1915 would be wood base. The fact that it matched the gun is another factor that leads me to believe that is an East German reissue; The mags were renumbered to match the guns. I have an E. German reissue, complete with the "X", so I figure that the Russians sent those back to Germany to fit in with their chain of supply so to speak.
The font on the takedown lever, being much larger than normal, was obviously added at a later date.
The "crown N" proof on the barrel was not right, either, and was obviously a replacement. (Possibly in 7.65mm.) I didn't get a close enough look at it to be absolutely sure, but an E. German Suhl proof is similar, but usually is accompanied by a date underneath to indicate when the barrel was installed. The dates are generally in the early 50s. Mine is dated 8-53.
I think the guy was offended by what he perceived as attacks, and is probably smarting from learning that his beautiful original collector gun isn't. but he's not the first and certainly not the last to have that happen.
At any rate, I believe he said he paid $900.00 for it, and, in today's world, that's still not a bad price to pay for a shooter.