It happens in gun stores too both A/ND and those who load rounds into firearms.
All firearms are always loaded!!! I have cleared, handed the firearm to a customer, got it back, cleared it, he says let me look one more time, I clear it and hand it to him and they ask why do keep checking the firearm. All firearms are always loaded teaching time.
Customer starts stuffing rounds into a 375 because he wanted to know how many rounds it would hold, didn't believe me or CZ; heard hollow points don't feed well so tested them at the counter; unholster his Glock and proceeded to dump rounds in the floor trying to clear it, he had no idea why the rounds kept feeding, he even said so while shaking his head in wonderment; reloader bring in his pet load and wants to test them in a new xxxx to see if his reloads feed before buying; and firearms do come with rounds in the chamber from the factory, I have seen it maybe 10 times in 17 years. My rule was no ammo on the counter period, it torqued a few customers and it wouldn't stop it all.
Seen videos with LE /BATF where some come in with loaded mag, ask for a gun, stuff the mag and rob / steal the firearm, run out the store with a loaded firearm.
During peak times, so many people at the tables it would be hard for the sellers to watch everyone so bring a good supply of zip ties. I have been to a couple with a rule that all firearms must be and remain in unfiring condition.
For what gun shows charge for a table/booth, its no wonder how much high markup junk they have to sell. I was checking out knives and every single one was made in China and priced more than a new Gerber. Last one I went to looking to check the market, there were as many non firearm related tables as there were firearms. And many firearms (used) were higher priced than a customer can buy at a actual gun shop.