BUYING HERMIT CRABS FROM PETSMART QUESTION?

Ok so sometime soon I plan on getting at least 2 hermit crabs from petsmart. My question is- do they have both male and female ones? Do they vary by store? Do they put each gender in separate tanks? I don't want to buy opposite genders. If you don't know what you get, should I research how to tell the gender so I can see before I buy? Thanks.