You know what? If you offered people receipts for taking their guns, I bt a lot of people would bite at this. The police get called all the time to dispose of guns that people do not want. Sure, some times they're just ghetto blasters that baby's momma don't want in her house while babby's daddy is in prison, but many many times they are good guns, owned by the widow of a shooter. She doesn't want them, but she also doesn't know how to get rid of them legally and safely. I have saved many a 1911 by telling her that:
1. You can sell it legally, here's how.
and
2. This gun is worth several hundred dollars, you'd be foolish to destroy it.
many times they just want the responsibility of it off of their shoulders ("what if it is used in a crime?"). Taking the gun and giving them a receipt stating that they no longer own it would probably be sufficient.
Mike