That sucks
, I know every time a snake dies you get a sense of anger and sadness in one package, best is to see it as a lesson and move on, I lost a few reptiles in my live, working with animals isn’t one of the easiest things to do.
Best is just to stick with us on sa reptiles, I have one friend that I trust with my snakes because I know him for a while, he's animals are in great shape and I know that I can learn allot from him.
I always tell youngsters: Try to get a friend that knows more than you and stick with him, don't lend out your ears to some idiot that thinks he knows something.
Get a vet certificate and show the store the results, tell them you know that there is no guarantee on livestock but the specific person gave you the wrong advice and that resulted into death, Tell him that you don't want a refund but a new snake if that doesnt work tell them you'll pay half the price, because you feel 50% is your fault for listening to that advice.
I know it's actually entirely their fault but I think that's the only way to get a replacement.