Pick of the Litter
This is an important part of getting a hermit crab... the inspection process. If you're getting a hermit crab for a child, you'll want a healthy one. How are you going to explain to your young child why his/her new hermit crab died 2 days after getting it? Most young kids don't have a grip on exactly what death is and it may be hard. So you'll want to get a good crab. After you've picked out a crab at the pet store, gist shop, etc. that you like, follow these steps to make sure it is healthy and ready to go home with you:
1) Check the hermit crab for tiny white bugs crawling on it. Those are called mites and they're icky, nasty, and deadly. They're what killed my entire colony of hermit crabs, and you don't want a single one of them anywhere near yours. If any hermit crab at the pet store has mites, every hermit crab in the tank has them. Go find a new pet store. Don't even think about buying a hermit crab there.
2) Check the hermit crab for missing limbs. A hermit crab should have 2 legs on each side, and 2 claws on the front. If a hermit crab is missing a limb, it will grow back when the crab molts. But the chances of the hermit crab not making it through a molt are greater if they hermit crab is missing a leg or claw, because it stresses the hermit crab out.
3) If there are dead hermit crabs in the same tank as the one you want to buy, leave the store. You don't know why those crabs died, but there is a good chance the live crabs will die shortly after you bring them home.
4) The crabs' enclosure should be free of flies or other insects. It should not smell too bad.
5) You should ask an employee of the pet store a question about the hermit crabs and he/she should be able to give you a straight answer. Sadly, most pet stores that carry hermit crabs have no clue how to care for them. They might feed them wrong, not clean the cage, etc. If the crab seems to be in a good state of health, by all means, get him out of that pet store.