Shelters are often staffed by volunteers who may or may not have specific training in behavioral issues. They DO NOT intentionally downplay a dog's problems to avoid euthanasia. Rather than a shelter, you might look for a rescue where the pup is in a private home instead of a shelter with other dogs. That will give you an idea of their true behavior. And just because you get a puppy from a breeder doesn't mean you get a dog without behavioral issues. Behavior is often an outward display of health, genetics and environment so if any one of those three isn't perfect, you'll have to work with the outward display.
I'm glad you've decided to pass on this one - it sounds like it's not a good fit.