Well there you go Melissa. It's bad enough they sold you a snake that was in no way appropriate for a family pet for a 12 year old (and your very small dog!) but they also sold you an enclosure that was meant for an aboreal species. I understand most aboreals don't make good pets either and are more for display but I could be way off on that information.
I'd certainly expect they should refund all your money for both snake and enclosure and re-train that employee. Having upset customers isn't going to help their business and perhaps the owners of this store aren't fully aware this person gives out incorrect information and sells inappropriate reptile housing. They should make good with you and they can always use that cage for their own stock, why should you be out even more money.
I know I'd be livid myself.
~~Joanna~~