A Dharma teacher leads through their ethical behaviour and kindness to others. These are considered to be the essential qualities of a Dharma teacher. A Dharma student might have a deep intellectual understanding of the Dharma and the exquisite aspects of emptiness, but without ethical behaviour and kindness to others they are not in a position to be a Dharma teacher.
There are other good qualities that we should look for in a Dharma teacher, but ethical behaviour and kindness to others are the minimum. For more information about the qualities that you should seek in a Dharma teacher, please see the chapter on the qualities of a teacher or relying on the teacher in a Lamrim text or commentary.
Practicing the Path by Yangsi Rinpoche
Liberation in the Palm of Your Hand by Pabongpa Rinpoche