It may be of interest to know that those contracts between rescue and owner are pretty much unenforceable in law, particularly when a payment has been made for the animal even though the payment is called a “voluntary donation".
The argument goes (and it has been tested in court) that whatever the exchange of money for animal is called, if the rescue cannot prove that they would have handed the animal to you anyway without money changing hands, then in law, the payment is not a voluntary donation but a purchase. Given that animals are considered as things, the fact that you have purchased the animal gives the purchaser almost the same rights over it as over a washing machine or a car or any other purchased item. I say “almost” because there are of course animal welfare laws that cover cruelty and neglect.
I am NOT saying that a 3 year old dog should be PTS, simply that a rescue cannot in law set conditions on what should happen to the dogs they rehome if money has changed hands in the process and if the dog would not have been handed over without the cash! Rescues can also no longer require that an animal’s microchip remains registered to them, they can still stay on as alternative contact if the owner agrees.