Goldfish help please how to get my money back?!?

I would freeze the body and keep the water. Then would test said water in front of them. If its indeed good, they will see it isn't your fault. If they still didn't believe you, I would bring in the body for them to test it.

Did you only argue? Know that its probably a private hobby and they can be courteous if they want to or not. They cant get fired nor is there a fear. I would ask to start over and calmly yet courteously go over the situation and try to point out what went wrong. Calmly yet assertively. If you come to a conclusion, try to figure out a deal. You get half your money back in exchange for a smaller fish or getting a replacement.

Next time you buy from a breeder with such a big number, I would get a written and guaranteed statement for the event if this happened again or the like. Also try and get a seal of health too on the fish

I'm sorry, you probably won't win this fight, there is no physical proof that the fish died on it's own and they most likely will not give you your money back... I would suggest being more considering of who might be selling you something. Because they could have easily known that fish was in bad health, anyway good luck.

You may can bring in a water sample proving that your water was not the cause of his death. If they know your water is good, It is there problem by fault.