Maybe because I don't have a lot of experience with pure-breds, but if I WAS looking for a pure-bred and had made myself aware of all the potential problems, the first thing I would be doing is to take the pup to a vet to get it examined for those problems.
For instance in the case of a lab, I know they can have hip problems, and I would hope that I would have seen the hip scores for the parents (not that I really understand what they mean, but would educate myself beforehand), and I think I would get the pup tested myself (if that's possible IYKWIM).
I don't know, maybe because I've been in rescue for so long, and read forums like these I'm a bit more aware of the hazards of potential health problems.
In response to the OP, I'd like to know at what point a problem was noticed? I ask because I am genuinely interested. However if it wasn't noticed until the dog was 8-9 years old, well, at that age many big dogs can start having joint problems, I'd think it was normal and would simply work with my vet to make the dog as comfortable as possible.
Or am I missing something here?