Yes, the face to face transaction thing is fine by Federal Law. It's the State and Local laws that will get you. What's fine in Idaho, might not be fine in New York, and what's fine in NYS, certainly doesn't fly in NYC, etc..... In general for the majority of non urban areas, same state(both parties living in state), face to face transactions are cash and carry for the most part. Out of state private transfers are to be handled by FFLs and are subject to the same paper work as regular in store purchases(NCIC, 4473 forms, etc....).
Personally, I wouldn't transfer a firearm privately without getting a copy of that person's state id.