Getting banned for life is the typical punishment. I'm not sure how they police it, or how long life really is. Maybe the life of the show. The promoter surely doesn't want them back within memory.
All promoters aren't created equally, either. I don't ever hold to my swearing I'll never go back. But 10 years was the time I remained away from the last show I heard a gunshot. It was the Goodman show up in Dayton, OH. A buddy wanted to go so we made a road trip. We were near the middle of the main floor when we heard it. Its kind of an interesting event. A floor in a 600 table gun show goes from chaos and chatter to dead silence in an instant. Better still, you can tell the training the attendees have received. About half hit the deck, the other half pivot in the direction the shot came from.

Then everyone checks himself out for bullet holes and leakage.
At that show we wandered back over to the scene of the crime. A black guy with a trench coat had walked in. When asked if he had a gun he just lied. Then walked down the front of the building asking every vendor if they wanted to buy a gun. When they got to the end table the good old boy asked what he had. So he pulled out his 25, dumped the magazine an snapped it at the floor. Except it didn't just snap. The real problem was the bullet came up off the floor and hit a girl in the leg. It didn't penetrate the skin or levi's, but it hurt.
The first order of business was keeping the boyfriend from killing the shooter. Almost everybody thought they should have let him. But Goodman was a jerk and didn't prosecute the guy. Dayton's finest arrived without much delay. The problem was they didn't see the convicted felon with the gun, having the rent-a-cops already securing the weapon. So they put the game on the promoters shoulders. He could prosecute for trespass, but he'd have to come back to town to testify. He declined. Which was how we felt about his gunshows. I'm sure it wasn't worth his time, and it would have just been a misdemeanor.
The message he sent was much worse.
And then there was the country gun show down in Corbin, KY about 30 years ago. We drove up to gunfire. Heard more as we parked and walked over to the entrance. When we asked what all the noise was about the guy taking the money was undisturbed. He said he guessed somebody wanted to test fire a gun they were looking at.

Yep, that was it. Out the back door into a hillside just beyond.

Worked well for them. Its why everyone likes country gun shows.
I've been to a few "barn sales" where the same thing was going on. A buyer wanted to see how a shotgun worked, so they walked over to a hayfield, loaded it up and threw a clay pigeon out for the buyer to shoot. Then the owner had to show it off a little, too. Truth be known, I think they were all having a good time. To the shock of a few folks at first. Just boys havin' fun. Another time a guy wanted to test fire a 22 down at a crick. Its no big deal. Its Kentucky, everyone here shoots guns.