If the dog likes you, I like you

Dog owners are famous for letting their dogs have an opinion about people they meet.
"He just didn't like George," one woman might say to her friend about last night's date. "He wouldn't go near him, and you know, to be perfectly honest with you, I just had this feeling that something wasn't right about the guy." Do dogs have a sixth sense about people? My answer is no.
Does this make your dog less trustworthy as a judge of character? My answer, this time, is only slightly different — mostly no.
Alexandra Horowitz in Inside of a Dog brings up the story of Clever Hans the famous counting horse. There was a horse, a long time ago, who was said to be able to do math. He would tap out the answers to math questions and always got the right answer.

Clever Hans, the famous counting horse

Eventually, it was realized that the horse did not know the answers to the math questions, but he was simply reading the response of the human asking the question to figure out when to stop tapping. Not even the horse's owner realized this was taking place, because he was blissfully unaware of the tiny body language signals he gave when the horse reached the right answer.
What we have to take from this as it relates to your dog's ability to judge the character of others, then, is that there's always the possibility the dog is not making a judgment of the other person as much as he is picking up on cues you're giving about how you feel about that person.
Perhaps in the example I started with, the dog owner was the one who had a bad feeling about the guy and the dog, an excellent reader of human behavior, particularly its owner's behavior, picked up on it.
This is called the confirmation bias. Horowitz writes: "Dogs become amplifiers of our own beliefs; we can attribute to them that which we think ourselves."
After all, how often do you hear people say, "My date last night was amazing, I've never met such a wonderful man before. But the dog didn't like him, so I'm not going to see him again."
You just don't hear that.
Now, let's return to the idea that dogs are excellent readers of human behavior. They are.
Dogs study us and they learn a lot about us, particularly our body language.
Horowitz writes: "We all have characteristic behaviors we display when angry, nervous or excited. 'Untrustworthy' people often glance furtively in conversation. Dogs notice this gaze."
So, could your dog be able to pick up on who is good, and who is not?
Probably. But the point is, if your dog noticed, you probably noticed it too. Humans just don't always consciously process why we get these feelings that we have about other people.
You instinctively know that darting eyes and shiftiness is body language that expresses some nervousness that essentially indicates the person has something to be nervous about, and therefore is perhaps lying or untrustworthy in some manner.
You just don't process it. You don't automatically think, "his body language is giving me a bad feeling." Instead, you just chalk it up to this feeling you had — call it a gut feeling or an instinct, whatever.
Your dog is seeing the same things you see, but processing them more directly. And he's also paying attention to you to see if your body language is confirming what he sees.
Can we rely on our dogs to be good judges of character, then?
Perhaps, but not because of some sixth sense. And their opinion can be very much influenced by yours, so a better option may be simply relying on your so-called 'instincts' in the first place.
Go with your gut.