Jim,
A quick observation about a dog’s ability to judge character or to determine a person’s intentions: They can’t, they have no clue; they are terrible at it. What a dog can do, however, is study their master. Remember, we are their world and the object of their attention 24/7. Your dog knows your thoughts almost as fast as you think them. After all, they have nothing better to do but watch you. So if your dog doesn’t like someone new, they are picking up that vibe from you, and acting on it. Your dog doesn’t care about hurt feelings or offending someone. I find this most beneficial.
I have noticed that after the person that I deem to be ok is around awhile, my dogs will start to reflect how that person feels about them. If the dog’s reaction is positive or negative I don’t put allot of stock in their behavior, as the new guest has passed muster. It is their initial reaction to a person I’ve just met that I’m sensitive to. It helps me to hone my gut feeling and to pay attention to it when my dogs aren’t around.
There is a book called “The Gift of Fear
I hope this is of value to you and your readers. – JM