SRILA PRABHUPADA: "Bona fide guru means he presents himself as servant of God. He does not pose himself falsely that “I am God.” This is bona fide. It is not difficult to find out bona fide. But this is the test. If anyone says that “I am guru,” er, “I am God,” then he cannot be guru. Because he has no knowledge. How he is God? But he can cheat some people. That is different thing. You can cheat all people for some time and some people for all time, but not all people for all time. That is not possible. So these kinds of guru, who poses themself that “I am God,” he’s a false guru. The bona fide guru will say that “I am servant of the servant of the servant of Krsna,” or God. Servant of. That is the business of guru. He serves Krsna as Krsna desires; that is his business."