One position being carried by vocal loud mouths does not have any bearing on the positions validity.
This situation is very clearly not clear cut. If I was the buyer in this situation, clearly had a handshake agreement in place, the seller demanded F&F, I had requested the insurance, offered to pay extra for the insurance, and then the seller sold it out from under me I'd be pissed too. Now, I'm not sure I'd be right to be pissed, but I would be.
The seller does not list accepted payment forms and then rejects a common and valid form of payment. I don't think this necessarily rises to the level of negative feedback, but the seller clearly has responsibility in the situation.
The manner in which he requests F&F, as presented to date, was shady and should be a red flag for a buyer. Now, he may be a great guy and didn't mean it that way, but from a 3rd party POV that's exactly how it comes off.
People on here arguing that F&F is SOP here was a surprise to me. I completely get their argument for it, but it was a surprise none the less. In my experience it's more common for forums to ban F&F. I say that to say this, it is unreasonable to expect the buyer to have known this is SOP here.