The breeders from whom I purchased dogs never used a written contract. And while the first dog I bought I finished and placed into my breeding program, it wasn't without issues. This is when I started to learn about honesty, disclosure and ethics.
Without getting specific about health issues so as not to point fingers (which is not my intent here), let me just say that my first champion came with plenty of issues that were not disclosed. Perhaps because these issues weren't known for the most part, perhaps not - I don't know and never will. One would have to actually health test to know what they had and what they were selling.
Finally, if you are lucky enough to find a show quality bitch or dog (I know - I said not to buy a dog) with which to begin your breeding program, honor your word and your contract and if you can't, let the breeder know so arrangements can be made. Events have consequences, so if you can't keep up your end of the bargain, or choose not to, communication is the key. And if you're the breeder of that dog, work with that person and honor your contract or negotiate a reasonable return. It should be about the dog - not about you. If you make it about you or about the other party, your contract and/or your intent probably isn't about the dog anyway - shame on you.