Individuals must ship to an FFL, some will argue that they must ship from an FFL to an FFL.
I've bought a few from individuals on GB, I checked their feedback before bidding, and made sure that there was lots of feedback on them, and all good other than individual misunderstandings. So clear up all details before bidding/buying.
I've never dealt with an Armslist seller, and by how some of them think their used beaters are worth new retail +, I don't think I will dealing on that site.