If they say "I am a fan of Tesla", would I be right to believe that they are not a fan of Tesla?
What does "not a fan" mean"?
you would not know if they had never heard of Tesla, are still on the fence about tesla, or whether they dislike tesla.
Typically when someone states "I am not a fan of..." They dislike the subject... So your reliability is not there.
And I won't go back and find your post, but you stated you would know "100%" of the time. Here you can only be sure he has never heard of Tesla, dislikes tesla, or is undecided. He did not tell you what he was. He told you what he was not.
It is as if he told you he had five fish. he could have zero, or one, or six.
You know he does not have five fish.
please consider what you wrote.
EDIT
OK it was easy to find your post:
"A person who lies to me 100% of the time on the other hand is a very trustworthy/reliable person. I would know what to believe after listening to them."
in your scenario you do not know what to believe, only what not to believe.
Enough said.