I would take that snake back tomorrow not Tuesday, demand a full refund, and never set foot in there again.
They would also be put on blast on the FaunaClassifieds BOI as well as every review page (e.g. Google, Yelp, Facebook feedback groups) that I could find.
It's pretty much a given that if a store has mites then everything in there will be infested, simply because the snakes are living in close quarters, and customers/employees don't scrub down each time they handle a different critter.