National Instant Check System
All Federal Firearm Licensed (FFL) dealers must follow the provisions of 18 U.S. Code, sect. 923(a). This includes conducting an FBI National Instant Check System search on any purchaser of any regulated firearm, including at a gun show. It must come back approved before a sale can be made.
Private Sales
In most states, a non-FFL owner of a firearm can sell the firearm to another private individual at a gun show without going through a background check for the buyer. If the private seller has reason to believe that the buyer is not authorized to own a firearm he is forbidden to sell one to him. A non-FFL private seller of a firearm cannot access the FBI system.
State Laws
Six states currently require non-FFL sellers of guns to use the service of an FFL dealer who performs background checks to transfer a gun to another individual. These are California, Colorado, Illinois, New York, Oregon and Rhode Island. Connecticut, Maryland and Pennsylvania require individuals to transfer handguns through an FFL dealer.