If your puppy becomes ill or dies during the first two weeks and a licensed veterinarian writes a letter certifying the problem existed before he was sold to you, then you can return him for a full refund.
You need to understand that this does not cover accidents. Also, the worst puppy diseases have an incubation period of less than a week. A communicable disease that does not occur until the second week may be the result of your puppy being exposed to other dogs after he is with you, so a veterinarian will not certify that it existed when he was still here. The guarantee relies on the vets opinion.
I have always lived in a isolated location where my dogs do not encounter any strange dogs. This is the opposite of the health conditions at a pet shop or a large breeding or showing kennel where many dogs are able to exchange germs with dogs from other places.
If your puppy goes lame from hip dysplasia or develops a heart problem or suffers from some other serious genetic problem during the first 6 months and a veterinarian certifies it, then he can be returned for a refund or if you prefer we can work out other arrangements that involve him staying with you.