Contracts & Guarantees
Get everything in writing. Get copies of every health certification of parents.
If it sounds too good to be true, it is.
No bloodline in any breed is "100% free" from problems inherent in a breed.
No one can "guarantee" anything.
Realistically, most "guarantees" are really a promise of replacement if something goes wrong with your puppy after you buy him/her. Even the most conscientious of breeders cannot predict if your puppy will develop certain unknowns ie:hip dysplasia, eye anomolies, spine disease, or other unpredictable elements. What they CAN and MUST do is screen the parents for these things and then breed only healthy animals. This WILL reduce but NOT eliminate the risk for the buyer.
YOU as the buyer must educate yourself to the most common health problems in the breed you wish to purchase, and then only buy from breeders who screen and certify their breeding dogs to be free from these health concerns.
A reasonable guarantee will promise to replace your pup with an equal or better pup upon availability (meaning the next litter) if a problem arises within the first year. e.g. congenital defects, crippling defects. Some guarantees extend for longer periods and more defects. A few will refund your money, but common practice is to replace a pup with a pup. Many breeders will demand the return of your pup, however a good breeder understands owner attachments and will usually let you keep the original dog, and, after receiving a certificate of spay/neuter, will either give you a pup then, or, give you one when you are ready. (Be ready, though, to understand that they may no longer be breeding years down the road if you choose to wait).
Good breeders guarantee you they will help you find a home for your dog, should the need arise. They usually will not buy the dog back from you, but they also will not re-sell the pup to someone else, they will simply place it in a good home. (they may get a small adoption fee to cover the cost of Health Check for the new home)
The good breeders I know, and there are many, really want their pups and the new owners to work out. Both sides need to represent themselves honestly, and remember it's a living, imperfect being they are dealing with, not a piece of equipment. Things can go wrong, despite the best intentions and efforts of both sides.