I've never had tummy troubles with any of mine excepting when they were ailing with something else. They always got scraps from the kitchen when I was preparing food, but since I am vegetarian those treats were always veggies. Particularly liked and enjoyed were tomatoes, green peppers, carrots, asparagus, broccoli, green beans, and dried pasta. Popcorn was also desired! As soon as the first kernel sounded off I would have a waiting audience! (microwave popcorn, no oil).
For years I used NRG dehydrated food, and my Basenjis were always eager to eat every bit of it. Turn around twice, the dish was empty. I have never had a "fussy eater" except when the dog was ill, so turning down food was always a big red flag.
Dogs have historically been scavengers. With today's close breeding many dogs seemingly can't tolerate the kind of food their ancestors had no issues with, but I also suspect that the marketing of dog food has a lot to do with how we view feeding our pets. A century ago, most dogs thrived on what was scraped off plates after the family had eaten dinner, and contrary to what dog food manufacturers want you to believe, most of those dogs lived long lives unless accidents intervened. When I was young the "average" German Shepherd lived to 15 years or more. Many farm dogs I have known have exceeded that age by 2 or 3 years. Not so common, these days! We also have many weird and wonderful diseases and disorders that didn't used to be seen often or at all. I remember when hip displasia first started to become common. Coincidentally (or not!) it was around the same time foals fed commercial foal feed started developing contracted tendons. Do I see a pattern here? Feed companies were all about fast growth, great for an animal you are going to slaughter and eat, but not so much for one you hope will last as your companion.