I never want to sell to the wrong buyer and have that on my conscience.
This is what I fail to understand. What does it matter?
I get the sentiment, the "Oh my, If I hadn't sold him that gun" thing.
But it's an object, you didn't provide motivation and if he is motivated he will find a way with or without your gun. I simply do not understand this idea that you can prevent these things without foreknowledge of his intentions.
That study I did of the 16 mass shooting that occurred in 2012, did anyone fail to get the idea that almost every one was completely unavoidable by background check. In at least 10 cases the criminal/madman wasn't a criminal or a madman until he started shooting people. Sometimes times it was with stolen firearms. Usually it was legally owned weapons from people who had no reason to be listed as prohibited possessors at all.