I have have four people I know who have had issues.
#1, A Golden who was showing signs of mild displasia at just under a year of age. The breeder ( a good breeder!) told them when ever they were ready she would give them another dog free of charge. They did collect on that promise a year and a half later.
#2 A Mini Poodle Golden X (don't get me started, I advised against it) Who at 4 months showed severe bi lateral hip displasia. She called ther "breeder" who told her she would say a prayer for him. The dog ended up having one hip replaced. The breeder finally agreed to refund the purchase price (1200.00) but the owner has never seen a penny.
#3 A Standard Poodle who had the day blindness (rod and cone disease?). This was not on the breeder's list of covered diseases, but the person was refunded their purchase price immediately and offered another puppy. The owner chose to keep the dog, and she lived a fairly normal life.
#4 A Black Labrador, who at 4 months started showing lameness in a front leg. The (well known) breeder insisted it was pano, or that she was playing ball too much with the dog. Eventually it was clear with x rays the dog had elbow displasia. When the breeder was given this infomation she told the owner to check her paperwork that she does not guarentee elbows. No support, concern, nothing.
It all depends on the integrity of the individual breeder. Get references!
I would say it all depends on the integrity of the breeder