I am sure you would agree to the idea of a gun license to keep arms, right mate?
I'm not GP, but yeah, actually.
The word "license" is a bit tricky, because it implies a bit of tracking and government oversight which probably won't fly in a business like gun sales. However, requiring some form of in-house training before sale of a gun wouldn't be a terrible idea.
As one option, we could require a certified gun-safety person administer the training (look, I'm making jobs!) Before you purchase a firearm, you and Captain Safety have to spend some time on the range. He/she would observe as you load, fire, clear, etc. Maybe it could even be similar to vehicle certification (i.e. your drivers license) in that there are different flavors. Just like I'm only licensed to drive a car, and not a bus, motorcycle or big rig. I'm only licensed for handguns, not shotguns, rifles, etc.
Just a few idea... but yeah. Having some mandatory training wouldn't be a terrible idea. And if someone is already familiar with firearms, the training would be a breeze. Just another day on the range.