Food intolerance can be a genetic flaw and that could have been the issue. I've never heard of the food being an issue as far as tear stains, but I've never took note of tear stains before either. The only food issue I've noticed is certain foods may give my dog diarrhea. That's why sometime after I got my dog, I changed the food that he was on (and had been on since before I got him). Now he's only allowed lamb and rice dog food, which is expensive, but it helps his food intolerance a lot. He is also not allowed table scrapes whatsoever. The most he's allowed outside of his dog food is dog treats and meat scraps that is for my chickens. All of those are fed on occasion, not every day.Ive never heard of food causing it.
Its mostly genetic is what i heard.
We were looking at a litter of puppies, the grandsire had a tear stain, which caused a puppy out of the litter, the one that we were wanting to have them. But i didnt like the genetics of them so we didnt get him.