It isn't quite the problem that it used to be before the sales of guns were as well documented. If I tried to claim that his gun was really mine and that it was stolen, then all the authorities would have to do is check with the store's paperwork where it was bought. But if it was an older gun or the individual couldn't locate the person he had bought it from then he might have a problem.

Imagine being stopped late one night while packing a gun that you had posted the serial number on the internet. The officer asks if there are any weapons in the car. "Yes officer, I have this gun that I've owned for years". The officer says "I'll need to check the serial number please." The gun is handed over and the officer checks it in his database.

Oops, I took the serial number that was posted on the internet and reported it as stolen from my car last month, right after you posted it on the internet. Now, I'd like to be a fly on the wall while you try to talk yourself out of being arrested for possession of a stolen gun. I wonder if you have any paperwork with you in your car that shows you are the rightful owner of said gun. I kind of doubt it. Looks like we have a problem Houston!!!!

...Hey it could happen...