I'm gonna append to my previous post.
Since I remembered that I've also purchased one and sold a couple of other guns FTF. And didn't use a FFL holder to accomplish either transaction. But those were all many years ago, before I knew what I know now. (Oh, ignorance can be bliss, till it bites you in the nether regions.)
That said, both of those deals were done via duplicate copies of sales receipts, signed by both buyer and seller. Purchase was done from a friend for a rifle I knew was clean; sale was for that same rifle several years later to an unknown person (answered an ad in the paper) at his residence. Multiple guns on display [wisdom of that is not at issue here], so I felt fairly certain it was a clean sale and he was legal to own. Upon consumation of that sale, he asked if I had any other guns I might be interested in parting with, and we came to a meeting of the minds on a cheap .22 revolver I had. Again, bill of sale, duplicate copies, and all was well. No federal or state paperwork, but we both had evidence if necessary of where the guns came from or went to.
Given the same circumstances, I'd do all of the above again with no changes. However, selling to someone I don't know, with no other way of knowing they're legit to own, I'd probably want to use an FFL holder and do the ATF paperwork. If they have a CHL, in a FTF deal, I'm good - that tells me they've passed inspection by the state and they're legal to own. Just fill out duplicate copies of a bill of sale, and we're good to go.
That last part mostly deals with selling, though. When buying from an unknown party, unless they can show me the purchase receipts from XYZ store, I think I'd want to use an FFL holder to make sure I'm getting a gun with a clean record. The last thing I want is to purchase a gun, then for some reason (sale, trade, use in a SD situation) have it get checked, and have it turn out to have been stolen.