I buy predominantly online from hobbyists/hobby breeders. I like seeing the exact animal I'll be buying over some of the bigger sellers who sometimes use stock images for their animals and have "met" a lot of great people this way. Checking references on Fauna's BOI is key though too.

I have bought from larger expos (no local monthly ones here, I usually go the the Phoenix Reptile Expo in November) and have had 50/50 luck: I got two snakes from one vendor one year who both came down sick and that made it where I'm cautious about who I buy from at the shows. But the other snakes I've gotten have been fine: also met some great people this way and it's a plus to be able to see the snakes in person first before purchasing.

Also have bought from two local breeders with great success, it was really cool to see their set ups and their personal collection as they were nice enough to invite me over.