This question is in the mind of any sincere or serious potential Yoga Teacher. Unfortunately, such persons have only few options available and many of them do not prepare them to be a teacher. This leads to confusion or frustration. Sometimes, very good potential teachers give up their dream and take up something else.
If one wants to become a Mathematics teacher for a high school, he/she knows that he/she has to obtain a degree or even post graduation in Mathematics to get such a job. Such a Mathematics degree requires one to know several other subjects than just Mathematics, such as language, presentation, communication, and management of students. If they want to get a job at very good schools or higher grade students, they have to do even better or more education.
In the similar way, a Yoga Teacher has to get sufficient training in Yoga and associated subjects in order to be employed and be successful in the Yoga profession. Since Yoga deals with practice in addition to theory, one has to do sufficient practice of Yoga in order to become credible teacher. If one lacks skill for management of students, one will not be a successful Yoga Teacher.
Such kind of training is generally not available at Yoga studios or Retreat Teacher TRaining programs. One has to meet a successful teacher and spend time with that teacher. Such a trainee should practice Yoga regularly for sufficient time. How much time is needed in these two cases depends on the student and also the teacher who guides them. However, only a well established teacher should certify a potential teacher (trainee) to teach.
Unfortunately, competitive and commercial set up is going to mess up everything. But, at the same such a set up is unavoidable in today’s times. Therefore, a serious and sincere trainee should make sufficient efforts to find proper resources and spend sufficient energy and time to become as good teacher as possible. They must not be complacent of certificates and they must not rely on advertisement without verification of the sources in person. Such verification should be done in person if possible, and not through inexperienced friends or teachers.