There are three basic ways. First way that God tells you whether or not someone is His representative, the first way is from within the heart. From within the heart He tells me, He confirms to me within that, “What this person is saying is true. This person is My representative.” Not just that, but actually helps me experience from within my heart that I could place my entire life in this person’s hands and in doing so, I am placing my life in God’s hands. Okay? I’ll have that vision from God.

For the soul there is never birth nor death. Nor, having once been, does he ever cease to be. He is unborn, eternal, ever-existing, undying and primeval. He is not slain when the body is slain.
BHAGAVAD GITA 2.20