I see stuff like that all the time, but Petsmart and Petco at least always have thermometers and hygrometers (they're dials, but nonetheless) in their displays. Is this a privately-owned store?
I honestly wouldn't recommend buying it to "save" it. Instead, pressure the store owner to fix the situation. Tell him that you're not willing to buy the snake in this condition and ask more questions about its husbandry and health. He probably won't like you, but maybe he'll learn something about customer satisfaction... or better yet, an animal's well-being.