When the proof house rejects a gun and obliterates the proof marks it is usually because it has been submitted 2 or 3 times and keeps failing proof. It would fail proof because the barrels were rivelling, the action coming off face, or perhaps even cracking. You might want to check all those things before considering a purchase.The gun was probably dumped out of Britian or Europe because it was illegal for sale there.

Better to keep your mouth shut and be thought stupid,than open it and confirm.