if that private individual rents tables at 6 different shows a year, buying and selling at each one, then a good argument could be made that he's "engaged in the business" and required to have an FFL. Engaging in the business without an FFL is already illegal though, and won't be cured by universal background checks.
Yes, this is what my Buddy claims he has seen and he made a very good case for requiring NICS reviews of all transactions at a gun show.
However, it also sounds like there are already rules in place and maybe this just falls into the lack of enforcement category. Of course it could also fall into the “Buddy exaggerated” category.