Maybe he got scared off when people started making assumptions.
I don't think there's any way to determine who is at fault in this case. We don't know enough about the interaction, the buyer, or the seller. For all we know, the seller could have led him astray and told him the snake will not get very large, or that it will be easy to care for. Possibly the buyer said what he had in mind for keeping/caring for the snake and the seller said that it was adequate. If you're at a show, it's harder to do research because once you walk away from the stall, that snake could be sold. Given, they could have waited and found another snake, but some people believe in love at first site. Anyone who cares about the animals they breed and sell will give as much information about the animal as they can, and do their best to ensure the animal well be well cared for rather than just making a sale. Once, when I attempted to purchase a pair of sugar gliders, they gave me a 2 or 3 page form to fill out asking me how I would feed, house and take care of them. I realized I couldn't do it. Good on them, they lost a sale but saved their sugar gliders from a possible bad situation. Despite efforts of good animal breeders, the animals can still end up in bad situation because the sellers have to trust their own judgment on a perfect stranger - which may not always be right.
I am glad this OP is at least trying to find out information to care for his new pet at least.