Thanks for all the replies! It looks like the consensus is that corns should NOT have crickets in their enclosure, so I will tell somebody next time I'm there... probably that cashier I mentioned, as she knows more than their stupid (and fairly rude) manager.

Btw, I'm thinking of getting a corn snake soon - but not from Petco, LOL. If I can't find one at the GOOD local shops (EB Vivarium, Coastside Critters, etc), I'll just go through an online breeder. Looking at the available corns on VMSHerps site now, since I was happy with the leos I got from them.