Ask yourself this question , someone comes to your home buys a dog takes it home and decides for whatever reason they don't want the dog. As a breeder you are obligated to take it back as it is not a shirt that doesn't fit but a puppy Those people have wasted your time and money We require that the new owner take the puppy to their vet within 72 hrs for a well puppy check which begins a relationship between a new owner and their puppy. If they don't there is no guarantees. My guess is there is more to the story. I have seen young women come buy a puppy and take it home only to find out that their male dude boyfriend tells them it has to go. I don't know why this happens but it is not uncommon and what happens is people will lie and say something is wrong sigh it. People are liars. My guess is this person treated the puppy with an online diagnosis and made it worse which the experienced breeder recognized. As a breeder of 22 years we have heard and seen it all.The problem is in this case the breeder is keeping BOTH the money and the dog. That is just wrong. Also unethical, and probably illegal. Plus to say they heve proof that the buyer deliberately tried to kill the puppy is just nonsense.