A common thing I have seen lately is also receipt issues.
At a show, it can be something that's difficult to get, but if you can, ask for a receipt for the transaction. That way you have written proof that you purchased that hatcling from said vendor, just in case there are problems down the road or issues.
Expos can be very hectic, and I know only a handful do this, but it should be a request that most vendors should honor. Receipts are a standard of being in a business. And there have been numerous stories lately where a receipt might have helped resolve a potential problem, or back up a claim from the buyer.
All in all, go with your gut. If you get a 'bad feeling', trust it. It's usually right when it comes to that kind of thing.
Thanks! We don't have any reputable breeders/shops within 5/6 hours of here, and the expo is 4 hours away, but I thought it would be better than getting a sick snake. I didn't want to order online, either.