If there are 2 types of person, either 'A Person of Faith' OR 'of Doubt' how could either 1 discover is they're mistaken using each attitude?

By examining actual evidence, which is what a person of doubt will do, while person of faith won't do it.

As an atheist, I sometimes have doubts, but when I do I always think of Einstein. Most theists think of Einstein as one of them because of his famous phrase "God does not play dice with the universe." but Einstein only believed in God as a kind of basis for the laws of science by which the universe functions, he did not believe in a personal God, a mythical figure who had any interest in human affairs or who could be reached through prayer or faith. If I had any long term belief, this is what I would go for, all these ideas from organised religions, prayers and hymns, Heaven and Hell, angels and demons, are just total rubbish. They only exist because most people are sheep and cannot think for themselves.

Although a lot of religious people practice blind faith, biblical faith is not a lack of doubt, or centered around a degree of psychological certainty. It is a choice to walk in trust in the very face of doubt.

I cannot think of a single instance where some amount of doubt is "unjustified". That sounds like the blind leading the blind.

I think your argument would be even stronger if you had more random words in all caps.