You earnestly believe that you know Johnny’s history and that he is a felon, but what if you’re wrong? What if he ended up pleading to a misdemeanor, or got off at the last minute for something. Well you tell someone that he is when he isn’t, that’s slander.
The furthest I’d go would be to ask the seller if he has much experience selling pistols in NC and understands the legal requirements. If he says no I’d suggest that he google “pistol purchase permit” or “pistol transfer NC”.
But it sounds like you’ve solved the problem, and at this point I sure wouldn’t go looking for trouble.