There have been so many inspiring (and soul crushing) things said here and I have hardly anything to add, but I just wanted to say that despite being very responsible in searching for my puppy, she's still sick. I don't say this to refute what others have said about the importance of choosing a breeder that tests, rather I want to note that I stand by my original decision to support a responsible breeder. I quoted Sins comment above that your chances are lower of getting a sick dog if you get it from a responsible breeder and despite my misfortune I still completely maintain that this is true. I have heard from many people around me since my puppy got sick that I should have expected this with a purebred dog and that I should have just adopted a rescue instead (since many seem to think the chance are bad either way), but again I truly believe in the comments that many of you have made - that we need to be part of the solution and we can do this by carefully choosing where we get our dogs. I am sad for the potential problems my Rigby may have, but I am not at all remiss that I supported an ethical breeder.
The reality is that you are far less likely to end up with a very sick puppy,if you choose a reputable breeder who breeds with the welfare of the parents and the puppies as a major concern.
Healthy parents are more likely to produce healthy puppies,and if a breeder can't verify the health status of the parents,then they're not breeding for health or for the benefit of their customers.
By choosing a health focused breeder,you can stack the odds heavily in your favour and remove the "lucky dip" element.
No breeder can 100% guarantee that a living creature will be free from defect or illness,but they can try to do all that is reasonably practicable to put systems in place to reduce the likelihood of some early onset inherited problem happening in your pet.