Some very valid arguments have been made and I would like to throw another one in the mix for consideration.
Every time I have made a transaction on KSL I request a written receipt with name and serial number of the firearm and name and DL # of the seller/buyer. Why you may ask? Most importantly, to establish a timeline of when I took or released possession of the firearm.
In the case of me making a purchase, there are several unknowns. First being, I do not know if the firearm is stolen. Second, I do knot know if it has been used in a crime and lastly, I want protection from the seller claiming it as stolen or missing. For a number of reasons, the firearm may be ran through NCIC by a law enforcement. It would be the start of a bad year if that firearm was to comeback linked to a crime or reported at stolen. In such a case, the receipt could go a long way in establishing when you took possession and who sold it to you. On top of the receipt, I also print the listing from KSL. Of course, this documentation would be presented by my lawyer in my defense.
Likewise, during a transaction where I am the seller, I take the same steps as I have no control over the firearm once it has left my possession. For all I know, the person I sold it to could give it to his restricted person or use it him/herself to commit a crime. If and when caught, law enforcement will be asking may be asking a few questions. It would again go a long way for your attorney to have the paperwork mentioned to mount a defense.
I know of one case with a family member in Seattle who bought a firearm from a fella who later reported it, alone with a few others, stolen to his insurance company. Several years later, my family member's wife became seriously ill and he needed to generate some serious cash for her treatment. He sold almost all of his firearms to an associate who owned a pawn shop. As per law, the pawn shop reported the transaction to local law enforcement who found the supposed 'stolen' firearm in their NCIC search. On top of all the other angst in his life, he had to deal with this problem. In the end, it worked out but it took over a year to get it all cleared up. Unfortunately, his wife passed from her illness.
At days end, we all have a different take on the best way to go about such transaction but wanted to give a little food for thought.