25 + years ago when I was working pest control, one of my monthly stops had a chow. When I stopped there he was friendly, but not overly friendly. Greeted him, did my job, told him bye, and left. Later the other techs asked me how I handled that mean dog. Sometimes they just know. Many animals accept me as one of their own and I try to accept them as they are. I have met aggressive dogs, usually the small, overly inbred dogs or dogs that have been mistreated.
As to our current dog, Sasha, is a rescue from a probable puppy hoarder. Just under 50 pounds, may have growth stunted some from early malnourishment, color, short hair, and lose skin of a redbone, some head shape of german shepherd, and deep, narrow chest of a greyhound. Play fights with our cat, another rescue, JaqJaq, when they are not sleeping together.