Sri Sri Ravi Shankar:
Well, I never spent time looking for one! You know, your heart tells you. There is something called as the gut feeling. Your heart tells you that you are in the right place. Second is, any teacher, any master, anybody, even you as a friend, what do you want from your friend? Do you want something from your friend, other than their own happiness?
If you expect something from your friend or your student other than their own progress and happiness then you are not a good teacher or a friend. In friendship you expect your friend to be grateful to you but a teacher does not even expect that. So want nothing from anyone other than their own happiness. In the Upanishads, it is said there are five signs of a Master. The Upanishads have said that there are five signs of being with a Master:
1. Knowledge flows
2. Sorrow diminishes
3. Joy wells up for no reason
4. Talents come up
5. Lack start disappearing, abundance dawns