When spiritual teaching is harmful

Contemplation of the obstacles and delays that seekers must traverse to attain freedom from duality suggests that teachers have a great responsibility,
and one that is not always upheld. I can see that an entire system can be devised to understand this. There is precedent, especially in older texts, all of it out of the mainstream. References to that material will make for another project.
From my experience, teachers can cause harm actively, by conscious deceit, or passively, by teaching from a state of delusion. There is no doubt to me that a teacher can honestly believe they are awakened, yet not be because they don't have the capacity to adequately self-inquire. There are the "lesser teachers" as I call them, who have a real awakening, are honest and even humble, but have not or will not deepen enough to accomodate the awakening of others. This is like the bird being pushed out of the nest before it can fly.
The harm itself can be readily categorized. Traps of Adyashanti come to mind and he described them well. Extending this understanding can give further clarity, for example:
Delays in awakening - seeker is ready but the progress is slowed by a teacher who is inadequate, eventually the student awakens on their own or with another teacher.
Obstacles to awakening - the process is completely blocked for some length of time, even an entire incarnation. The student is dedicated or deceived by the teacher, sticking to the relationship and cannot make progress.
Regression from awakening - the teaching is divisive and leads away from nondual awareness. This could be in the form of neglect or abuse that fragments or compartmentalizes perception. Various forms of mind-control, and cults come to mind.
Currently, poor teachers and teachings are informally acknowledged by word of mouth or individual opinion. This results in confusion and allows the delays and obstacles to continue. Most seekers lack wisdom and discernment to determine who can effectively pull them deeper.

This is just a kernel, to be developed later. Recognizing those teachers or teachings that are innefective or harnful is one less reason for a seeker to stumble or delay in finding the direct experience of infinite awareness.