If you haven't already, cash the check.
If you end up getting the gun back, you can refund him what is due him (which will only be the cost of the gun). If, say, the ATF gets involved and takes the Anaconda into their protective custodial labyrinth, and neither you nor anyone else ever sees the gun again, you will have been paid just as you should have been. Pay no heed to the fact that the buyer keeps insisting this is between you and his FFL and does not want to step into it. He stepped into it (or should I say stepped in it) when he chose an ignorant person to have you ship the gun to. Maybe he couldn't have known the (in)competence level of his FFL, but the burden of that due diligence certainly never rested on your shoulders.
I would let both of them know, too, that if you do have to get a lawyer involved, you will take steps to see one or both of them pay the fees.
If you end up getting the gun back, you can refund him what is due him (which will only be the cost of the gun). If, say, the ATF gets involved and takes the Anaconda into their protective custodial labyrinth, and neither you nor anyone else ever sees the gun again, you will have been paid just as you should have been. Pay no heed to the fact that the buyer keeps insisting this is between you and his FFL and does not want to step into it. He stepped into it (or should I say stepped in it) when he chose an ignorant person to have you ship the gun to. Maybe he couldn't have known the (in)competence level of his FFL, but the burden of that due diligence certainly never rested on your shoulders.
I would let both of them know, too, that if you do have to get a lawyer involved, you will take steps to see one or both of them pay the fees.