I do this a lot. In minnesota there are no restrictions for transfers as long as both people are legal to own firearms. IE not felons.
I have a standard form letter that I use. basically it says....
Date..........
Seller ........... who by signing below confirms that he has no legal restrictions to possess or sell the listed firearm.
sells to Buyer.......who by signing below confirms that he has no legal restrictions to possess or purchase the listed firearm.
the handgun/rifle/shotgun.... make.....model.... caliber..... serial number......
for the amount of ..........
seller signed..................
buyer signed ..................
witness................... (optional)
I have used this basic letter several (20 plus) times. I make two copies and have all the data filled out before I show up.... I sign both and he signs both and we each keep one. If I am at home when I do this or in the office I will make a photocopy of both of our DL's on the back of the form.
I just figure this will cover me as a legal document.
I have bought most of the private party firearms by either letting people/coworkers etc know I was a willing buyer, or by talking to garage sale people who had hunting vests, decoys etc on display. after talking to them If they feel like letting me know they have firearms for sale, I let them check me out with a call to a local police official who I know who basically says yeah, he will pay you and has no criminal record. I prefer private purchases. Buyer beware, Know what you are looking for and what are common failings for such guns. Sometimes you have to buy something you do not want to buy in order to get what you want. For example I once bought two POS Savage .22 autoloaders to get a Winchester 64 and a pair of model 99 Savages. But in doing so I was able to get three minty guns for under a grand, and two rifles that went to the pawn shop for 50 bucks each. I prefer to have the transactions done at my office (I own the company) or at their house if they are garage sale people or friends of friends. I will not go to bad neighborhoods...not going to do it...nor will I buy or sell to people who make me nervous...I will just say sorry, I had something come up.... and cancel.
I have bought a fairly good number of gun this way. hope this helps