While some of the customers may truly just show much, the other pawn programs do have customer screening which means only certain folks make it to the TV area for transaction videoing. I would not be surprised if they did not have a casting call for customers like Gunsmoke does for buyers.
They're all like Antique Roadshows (the English version) on testosterone.
My FiL was asked to bring a few of his firearms to an Antique Roadshow. It was set up well before the filming of the show. He was asked to bring in a .557 double, A Drilling (can't remember the calibers) a Tower pistol, and a Sabre thats been in the family for years.
He was then told to look surprised at prices.