I've had one puppy 'returned' in 20 years of breeding - that being said, he wasn't really a return as he never actually left (sale fell through the day before they were due to take him home).
On the other hand, my mum adopted her cocker from SA. They said they'd take her back in a heartbeat if there were any issues (dog had severe behavioural issues).
But there are rescue centres and there are rescue centres. I wouldn't surrender or adopt a puppy from one of the Big 5 if you paid me tbh - not with how poor their standards are with animal welfare and looking after dogs and matching them appropriately and being honest about behavioural issues - but I would to a breed specific one.
What I would add, which no one on mumsnet ever bloody listens to, is that a contract between a breeder and a buyer are not completely enforceable. If you have a dodgy breeder, you're looking at huge, long, expensive and time-consuming fight to return that puppy to them. Ditto, a breeder saying 'the pups have to come back to me,' - they don't. You're not gonna be hunting down pups in 8 years time making sure they didn't go into a rescue and you sure as hell aren't going to spend time, energy and money fighting it in court. It's all lip service.
Yes, I have a contract in place for pups I sell - but I fully accept that, at the end of the day, once the pups leave my care there is very little I can do and likewise if I ever turned around and refused to take a pup back (which I wouldn't) the buyer would have a hell of a time trying to get me to take the pup back if I refused.