I am getting tired of this back and forth, because it seems to me that you are reluctant to accept some part of the blame for this debacle:
I said that you had accepted F&F payment. Which part of this is wrong or hard to understand? You did not ask for F&F in your sales thread, this I understood but the fact that he paid you via F&F, whether inadvertently or on purpose, still does not negate the fact that you ACCEPTED his F&F form of payment.
What you should've done then was to refund him his F&F payment and had asked him to pay you by G&S both for your protection and also his own protection. If he had thereafter gotten haughty or snarky with you, the fact that he had already not obeyed your rules as you had stated plus the fact that you had decided not to complete the transaction, would not have given him grounds to neg you.
Other than that, I am done discussing your self-inflicted neg feedback issues with you. Perhaps better luck next times.