I'm glad you spoke to them (the store) about this. I take it they don't breed them there at the store, do they? Really it's so hard to say what went wrong,
but it could even have been another customer or store employee that mishandled this snake, causing some sort of internal injury. There's just no way to rule
out something "contagious" though...too little to go on. I would give the cage a very good cleaning out, in case, but if a replacement comes from the same
place, it may have had similar exposure already. We'll just all have to cross our fingers for you...I do think they owe you a snake, & especially since you have
been their customer before. I take it that this is the first bad experience with snakes from this place? Was this the only rosy boa in their store? I would assume
they don't breed them, that they buy them from their supplier...that's why they didn't even have a birth date.