how are we going to determine what constitutes a proper training?
just brainstorming here...
training is required, perhaps basic gun safety training to purchase, and the "weekend at Gunsite" to carry in public?
For the first, put the burden on the seller. to provide the safety training with every sale. Cost included in the price of the firearm. The buyer can take the course or not, but pays for it either way.
To carry in public carries greater responsibility and might require one to have a higher degree of training in both safety and tactics.