It's already been explained to you, you just didn't like the answer and arbitrarily declared it to be a logistical nightmare. Nothing more than hand waving. The fact that you are trying so hard to find problems with this and have only been able to come up with such weak ones says it all really. I think the perfect encapsulation was when you said that we shouldn't background check people because those who failed it could become violent. Meaning that the alternative was we should just give those hair trigger people weapons without a check, lol.
If you just hand wave away common sense answers to your issues that's fine. You can't expect people to care much about what you ask for in the future though.
Unless you have a rigorously maintained national gun registry, Bozack is completely correct. There would be almost zero chance of being able to prove private party sales took place. All a person does is claim the firearm was stolen, and how are you ever going to prove that it wasn't? Are you going to mandate all stolen guns are reported. Now you're going to have gun owners just report their firearms as stolen, and then they can do whatever the hell they want with them. Add to that all the guns that are already in circulation, and it becomes a ridiculous proposition. It would be similar to trying to prosecute someone for burning a dvd for a friend. Yes, its illegal, but no one is ever going to fear getting prosecuted for it. In the case of burning the DVD, the law is really there to send the message that it is wrong, and hope that law abiding citizens won't rip DVD's as a result. In the case of gun sales, the gun sale itself isn't wrong, and so we aren't actually trying to prevent law abiding citizens from doing it. Just like with a private party burning illegal DVDs, I just don't see anyone ever being prosecuted over it.