I know four bad experiences with BYB - a friend's female boxer, her male golden retriever, and my sister's two boxers.
My friend's female boxer inherited major allergies. I mean major - I saw the report after she was tested - she is even allergic to poultry, which makes it extremely difficult to feed her so many things. (How many products have chicken as their primary protein source?!) We dog-sit for her often and have experienced how she can suffer if she accidentally gets into something here that is on her extensive list of trigger foods. She is on allergy medication daily that makes her sleepy for hours after each dose. She will probably need to switch medication eventually as this one is already becoming ineffective. They went through a horrific time when they first brought her home trying to balance out all her health problems, paid a ton in vet bills and almost lost her more than once when allergies had her throat swelling up. She is "stable" now but for how long? She is on such a limited diet and so prone to allergies, the fear is she will develop allergies to her regular diet, kicking off a new round of problems and suffering for her.
Her male golden retriever came home way too early - 5 1/2 weeks of age - and almost immediately showed signs of aggression to her children and husband! To shorten this story, the puppy bit both of the daughters by the time it was 10 weeks of age, breaking skin and drawing blood (one almost required stitches). It also attacked her husband and was unpredictable around her. In the words of a behaviorist I helped put her in touch with, she said this behavior in a 10-week old puppy was akin to a "6 year old human child holding up a liquor store, armed with a rifle" - it was that alarming. They tried to return the dog to the "breeder" who refused to take it back, and refused to refund their money. The puppy eventually went to a vet tech at their clinic, a person with no children that agreed to try and save the pup, although everyone pretty much said it would probably need to be destroyed.
My sister's female boxer, inherited allergies too - thankfully a brand and variety of food was found that cleared up most of the problems and got her off her medication, but for awhile she had itchiness and patchy hair loss among other issues. Briciola has also had several lumps removed already that so far have not been cancerous - but when the first major lump is removed before age two, you have to worry. She is now four years old and just had her first cruciate surgery on a back leg to correct a problem that the vet said is likely due to an inherited defect.
My sister's male boxer, Zucchero, inherited problems with both rear legs and needed major reconstructive surgery on both - the first surgery taking place at just 18 months. He was walking "stiff legged" most of his early life as he was barely able to bend his back knees. This also messed up his back conformation, he walked for so long with his hips very high (no knee bending) which created a "bowed" look to his back. I think the surgeries he had were for cruciates, one of the procedures was called "TPLO" surgery. Sorry I can't explain it better, but I do know they used a different technique on each leg, one more drastic than the other, where they had to actually saw the bone in half then "set" it to heal together again as part of the process. He also has pins and something like "fishing line" in one or both of his legs to help facilitate movement more similar to natural. The successive surgeries required not only lots of money, but a lot of restriction as far as playing and other social activities for a loooong recovery time. We are not sure if this is the cause of his eventual development of fearful behavior or if it is because he is almost certainly in some pain at all times, but eventually he became somewhat defensive and unable to enjoy playing with other dogs as he used to. He's working on this with a trainer now and showing great progress but it is hard to know that he almost certainly will be in some sort of pain every day for the rest of his life.
No more BYB for any of us.