Wait until he gets a crowd and then ask (out loud) "How did you manage to procure a license agreement for all those different brand logos? I want to sell stuff like that, too, but copyright violation is a federal crime!"
Repeat as necessary. Also, point out to the people running the show (or allowing them to set up on their property) that copyright infringement works it's way up the chain - and you have now let them know that willful infringement is occurring and they are no longer legally exempt from prosecution and lawsuits. If they continue to allow the sales of copyrighted materials they are willfully contributing to copyright infringement which places them in a very bad legal position.
I saw yesterday that Etsy stockholders are suing Etsy for allowing the wholesale infringement of copyrights and trademarks and they are afraid that if anyone sues, the value of Etsy will tank and they'll lose their investment.
I used to work part time for a computer store travelling around the Midwest setting up at computer shows to sell stuff. There was a company that we always jokingly referred to as the "Homeboy Computer Store" as they were very shady and all of their computers came pre-installed with Office, AutoCAD and other business software - almost as if they had been swiped right out of someone's office. They didn't include any discs, manuals, license sheets, anything other than the computer,mouse, keyboard, monitor. If you would ask them if they had something not on display, they would respond with "What you want? We'll get it for you..." One day there was a commotion at the entrance and dozens of black jacketed FBI agents rushed in and shut the whole show down. Every item they (Homeboy Computer Store) had for sale was seized, they were taken away in handcuffs and inspectors went booth to booth looking for other signs of copyright violation of AutoDesk brand software. We were lucky - we only sold hardware, so we didn't have a lot to worry about, but it sure brought that weekend to a screeching halt. Every time I see a booth like the one you pictured, I keep hoping to see a squad of FBI agents raiding them and taking them away...