Figure out which vendors are breeders and which are flippers. Skip the latter.
Vet all the breeders beforehand. Then make a list of those that have no, or very isolated and explainable, negative reviews and restrict your shopping to them.
If the vendor lets you handle a snake without asking you to use hand sanitizer first, hard pass. Even one mite seen is a very hard pass on the whole table.
Selection of animals at most expos is such that there is selection for the whole show, and many prices are negotiable for the whole show. I'm not in the BP crowd, but in general expos are a buyer's market currently.
I always go as a buyer early when the vendors are fresh and have some energy left to deal with me. By the end of vending, I know I'm pretty wiped out and not at my best.