Every single anointed person i've met has been odd. There is something wrong with those folks.
You ask, how do they know? Well they don't. They are simply so narcissistic that they feel they are special. There are people who really thrive on attention and status.
This is not too different than Geeshus himself. Image that, a hippie jewish carpenter, starving for attention who evidently knew jews were waiting on a messiah, so he figured that he was so special that he must be this person. And they believed him.
Now, how did Geeshus know he was the messiah? Well he didn't. He was just as narcissistic as the Jdubs who think they are annointed.