You’re wrong. Dealers operating even temp at a gun show are required to do a NICS background check before the sale by law. I’ve been to numerous ones, never been sold to without one.
The only way they’re a loophole is you can meet private citizens there to buy and sell with because yes, private sales are legal. Anyone smart selling private doesn’t do it without seeing a WCL and getting a picture of it.
He’s not, that’s the point.