They should sterilize everything they used for all the hamsters. Not just wash it, sterilize it completely. Discard any used bedding, and anything else that may have been contaminated.

I would also write to the corporate office for the store, with dates and receipts.

Sending the letter to the Better Business Bureau at the same time is something they should think about.

I would then wait a while before getting another rodent, and maybe opt for something sturdier, like a guinea pig.