Since the local pet shop says they have CB balls, maybe you should try to find out what breeder(s) they're buying from. It might even be someone that works there or something.
And the $50 is a pretty normal price. Like was already said, if you're getting an animal sent to you, you'll be putting lots of money into the shipping anyway, so you might as well get one locally if you can find a good one. And it seems like you can often trust a pet store that specializes in exotic animals over one that doesn't really know anything about them. Probably they'll even have someone working there that knows how to sex the snakes. Of course you probably should go to the vet anyway and get it double checked while your there.