There are millons of guns in this country and most of them don't have a paper trail to the owner so if someone wanted to sell a gun without a background check ( which would have to be done somehow electronically and cost somebody something ) who would know? So once again only the law abiding would follow the rules. Also the only way this would work is to resister ALL guns and how are you going to do that. And what most knowledgeable people think is that background checks on all gun purchases and transferrs will lead to the confication of any of those guns that later may be outlawed. It happened in California. The fear is real.