Good question Jon,
Under North Carolina law, it is unlawful for any person, firm, or corporation to sell, give away, transfer, purchase, or receive, at any place in the state, any pistol, unless the purchaser or receiver has first obtained a license or permit to receive such a pistol by the sheriff of the county where the purchaser or receiver resides, or the purchaser or receiver possesses a valid North Carolina-issued concealed carry permit. This requirement to obtain a permit prior to the transfer of a pistol applies not only to a commercial transaction, typically at a sporting goods store, but also between private individuals or companies throughout North Carolina. N.C. Gen. Stat. § 14-402(a)
If you do not get a purchase document from the purchaser, you can get charged with a class 2 misdemeanor.