Unless he is tailless he is way to small to be selling. SOunds like he is fresh out of the egg. If you are in the states, that is too much fo pay for a baby crested gecko.
Being so small and young, they can stress easily with too many moves. As it is, unless the store hatched him themselves, he has been through alot to be at the store. I suggest not buying him at all, or at least for a few weeks. Find out all you can about crested geckos before considering buying one. If it is still alive and has grown in a few weeks, is alert and active (though in a store, probably won't see him active as they are nocturnal) you could offer to buy him, or at least ask to hold him. If he wakes up and starts exploring (or most likely doing his best to get away from you, so be careful as they are real jumpers and with no real fear of heights) he probably is pretty healthy. If it just lays there and doesn't look alert (eyes closed, not very responsive etc) then he is probably not healthy at all and most likely will die if it doesn't see proper care).
One way to find out if the petstore knows how to care for crested is to read what you can, memories the key points and question the store workers about crested gecko care. Find out what they feed him, what size insects, how many, do they dust the crickets (or if they use a crested gecko diet, how often do they provide it etc.) If you see crickets bigger than the space between the crested gecko's eyes, most likely he isn't eaten at all or may have impaction problems by injesting crickets that are too large.
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PHLdyPayne