An attempt to use cold math to satisfy both sides of the gun debate.
Any dealer whose guns end up in being used in crimes more than two standard deviations above the mean*, must show evidence for why they are not at fault. The dealers will have some amount of time to provide evidence.
Any dealer whose guns end up in the hands of criminals at a rate more than three standard deviations above the mean**, must show evidence for why they are not at fault. The dealer's license will be suspended immediately.
This will require us to create a database of how many guns each dealer sells (what or to whom isn't needed), and use those numbers to find out the rate each dealer's guns end up in the hands of criminals.
Notes:
*2.2% on a normal distribution
**.1% on a normal distribution