Since we all have the Atman inside, truth will resonate if we are listening. It may be the "still small voice" against the trials and tribulations of the world, but it is there. With this in mind, listen to any teacher or guru that resonates, but keep in mind that the ultimate discernment lies within.
A teacher may be the greatest teacher on earth for a month or years, but you may outgrow the teacher. It does happen. When the teacher no longer resonates, seek out another, or go deeper inside. If you put someone above you, do it tentatively. Complete surrender can be a disaster if the teacher is on an ego trip.
The Atman is our own and it bestows upon us a liberty that gives us sovereignty. Albert Einstein gave a speech in which he riffed on the importance of individual liberty. He gave the speech on October 3, 1933 at the Royal Albert Hall in London. In it he said,
"We are concerned not merely with the technical problem of securing and maintaining peace, but also with the important task of education and enlightenment. Without such freedom there would have been no Shakespeare, no Goethe, no Newton, no Faraday, no Pasteur, and no Lister. Today,the questions which concern us are: How can we save mankind and its spiritual acquisitions of which we are the heirs? How can we save Europe from a new disaster?”
Einstein reminded the audience to keep clearly in mind what is ultimately at stake: "individual liberty."
If we listen to our inner voice, that Atman, we can trust ourselves to discern the lying fake gurus. Only follow that which resonates. David Hawkins calls spiritual teachers who purposefully mislead "Spiritual Rapists." Those are harsh words, but the spiritual seeker is the most precious of students, and they should have the best on offer.