My wife works at Petco. Just because one employee didn't know about them, doesn't mean they don't have anyone knowledgeable on staff. They feed once a week and don't always keep a feeding record because it's just too hard to tell different snakes apart that cohabitate.

Your best bet is to inform the stores manager. He's the one that cares if it dies (store will lose money). Also, all Petco's have vets for their region which doesn't cost the store anything. They would much rather have the snake make it, so they can sell it and make a 50%+ profit. Letting corporate know probably won't do anything.