For answers you can count on, you need a lawyer. Common sense and the law are not always 100% congruent.
I would point out that if the buyer cannot take delivery of the gun, then no sale has taken place. (common sense) If that is the case, legally, the FFL must ship your gun back to you (for which he can charge you) and you should (common sense) return the attempted purchaser's money.
HOWEVER, since the attempted purchase might be a crime, different legal rules might apply. Both commercial law and firearms law are involved and if you are facing this situation, you absolutely need QUALIFIED legal advice, not well intentioned internet advice.
Good Luck!
I would point out that if the buyer cannot take delivery of the gun, then no sale has taken place. (common sense) If that is the case, legally, the FFL must ship your gun back to you (for which he can charge you) and you should (common sense) return the attempted purchaser's money.
HOWEVER, since the attempted purchase might be a crime, different legal rules might apply. Both commercial law and firearms law are involved and if you are facing this situation, you absolutely need QUALIFIED legal advice, not well intentioned internet advice.
Good Luck!