Suppose my local friendly whoever has a "cash for guns" program and offers, say, $50 for gun turn-ins, "no questions asked."
Suppose I stand outside, and preview the guns coming in, and for the ones I like, I offer $75, providing I ask straight up, "Is this gun stolen or has it been used in a crime?" and get a "No." answer.
What could the police do about it?
So you can rob a bank, shoot the teller, get rid of the gun, and refuel the getaway vehicle. Cool.
They were paying cash for guns up in Rochester NY. They found out the dudes were using the money to upgrade.
Arrest you for disturbing the peace.
I kid you not.
Depends on the state.
Some states allow private individual-to-individual sales.
Some states require private sales to be “mediated” by someone (gun shop, whatever) with an FFL.