[apillar]

I know here in West Virginia, you can go to any of the larger flea-markets which typically occur one weekend a month during the Spring and Summer months, and there are people with tables selling guns, everything from an old hillbilly with 4 or 5 rusty guns to huge displays that would rival some gun stores. None of them require any paperwork (at least I've never found one that did). Then there are the actually "gun show's" which tend to be much larger and held indoors. The majority of these seem to require paperwork and background checks.

Honestly, I have no idea where they draw the line of what is a gun show, what isn't a gun show, what sales require paperwork, which don't etc.

[SampleMan]

...to huge displays that would rival some gun stores. None of them require any paperwork (at least I've never found one that did).

They are likely violating the law. If they are buying and selling for the purpose of making a profit (running a business) they require an FFL.

Many people at gunshows have run afowl of the ATF by claiming to just be "collectors", but setting up a table draws the ATFs attention, and they take note. If that "collector" is buying and selling too regularly, he is going to get cuffed.

[SoothingDave]

If someone has a huge display of guns for sale and shows them at a flea market regularly, then he is in the business of selling guns and should have an FFL.

If you are just selling a gun or two of your own on occasion, then there is no federal law against that.