no reciept required, but it might be nice to cya if you're worried about that kinda thing. Should be pretty easy to "size up" someone you're buying from and most in Idaho who do private party sales don't like doing paperwork.... duh... that's usually why they do private party in the first place. I bought a Remington 870 shotgun from a cop w/ out paperwork just over a year ago. :celebrate
Other than that just follow federal rules. Funny thing, nobody I've sold/bought from (and I've done a lot of both) has asked for ID, though one asked if I wanted a bill of sale and I said no... they were cool with it.
Actually, I'd be more worried about getting a receipt as the seller of a firearm. That weapon could be sold again, sold again, and then maybe stolen and used in a crime. Eventually, they'll trace it back to the store you bought it at and from there can trace it back to you. Nice to have something that says you sold it years ago.