Every reptile show I've been to has had plenty of snakes & lizards draped over peoples' shoulders, etc. as they walk around. I've engaged them, and while some are reptiles purchased at the show, others have been brought in for various reasons.
That said, I would not bring an animal into a show/expo. I would think one would want to vet the breeders/vendors whether you're buying, selling, or trading—ahead of doing a deal.
I would approach prospects, engage them in conversation about possibilities, and set something up later (or by phone/email) in a more... relaxed atmosphere, where clearer heads can prevail over emotions. Besides, IDT most vendors are there to acquire/trade; for the majority, this is their business, and they're there to make money (sell).
Alternatively, if the show has a website, they usually have a vendors list. You could try contacting vendors ahead of the show to arrange an appt. around the show (but not necessarily at the show).