How do we know the difference between superior teachers (maha-ácariya) verses inferior teachers (omaka-ácariya)?
I find in my 40-year contemplative life that it is very important to unpack our belief systems, especially those of mainstream religion.
Typical of the inferior teachers (omaka-ácariya) is either a complete disregard for the superior fruit of attainment (maha-phala), or complete misunderstanding of what they are. Typical in Buddhism is the inferior teachers (omaka-ácariya) tend to believe that the superior fruit of attainment (maha-phala) are nothing more than practices or techniques. A typical representation of this inferior understanding of the dhamma is a belief that insight (vipassana) is one meditation technique, and the religious experience (jhana) is another. Whereas, the superior teachers (maha-ácariya) understands that both Jhana and Vipassana are "superior fruit of attainment" (maha-phala), as described in DN-2.
Any Buddhist teacher who does not recognize or value the superior fruit of attainment (maha-phala) is at best an introductory teacher, or inferior teachers (omaka-ácariya). Therefore, if anyone wishes superior fruit of attainment (maha-phala), then that person must seek out a superior teacher (maha-acharya). Maligning a superior teacher (maha-acharya) only proves one to be a fool.