As others have said, it seems that the system just needs to be changed, and it would benefit everyone involved. They wouldn't have to "police" as much, and the attendees would be more aware. It just sounds like most people didn't know the "policy" that payment needs to be made prior to turning off a machine, much less a receipt provided as proof. If they want to address this in the future, make sure all vendors get a nice bright neon paper when they walk in stating this, and perhaps put a few signs up. Implement a tag system where you get a tag to tie to your machine when the $25 is paid. And again, most importantly, make sure everyone is 100% aware of the procedure. It sounds like poor communication more than anything else, especially if organizers are demanding to see a receipt and the people working don't even realize they need to give a receipt.

Yes, but that's IF the pin sells. Also the seller has to pack and haul the pin up to the show (and possibly back), and allow potentially a lot of people to play it for free, and maintain it while there if necessary. I think your post is a little bit slanted that the seller is getting a free ride and not doing anything. It's kind of like if you are the buyer of a pinball machine out of state, and you have to pay to have it shipped to you. No one is exactly complaining that you as the buyer have to both pay for the machine, and pay for shipping. That's how it works. If the buyer wants to take the machine early, then they have to pay $25. If they don't want to pay $25, wait until the end of the show per the rules.