There is only one guru — Krsna, the Supreme Personality of Godhead. So those who simply repeat His words, they also become guru. But of course a guru never thinks himself as being God. He only thinks himself as the servant of the servant of the servant.
From Srila Prabhupada’s letter to Mr. Himtsinh J. Bhatia, Mrs. Manjula H. Bhatia — Bombay 23 November, 1975