I know of a situation in which people coming to a class were having difficulty in getting a working sense of levels within levels. They were practicing quiet attention. Rather than pursue that more, a Teacher took the opposite approach. He put on several noise-making appliances at the same time. In one room were several radios, a tv, a stereo, and an alarm clock. The volume of each one was set so that only the loudest and most active could be heard. Attention therefore went to that. When that item was turned down, another came in to awareness, and so forth, until there was nothing on. The end result was the excess noise helped convey the lesson of quietness, the tricks the outer attention and the active mind play, and a better sense or feeling for moving from one level to the next more refined one.
A similar approach was taken at another time. Here the example was to feel getting larger - more than the identification with and attachment to one's body as one's self. The exercise was to concentrate all one's attention in the tip of the little finger and identify oneself with and as that. Then to slowly move back into the fingers, hand, arm, etc., identifying and focusing on larger and larger parts of the physical body until the person reached the whole body. Then the next step became apparent. In letting go of the identification with the body to that which is more, and so forth, identification could go beyond the body and one could then become more in ever refined and larger steps. If you were to have come in to either setting without the background and understanding of what was being done and why, it would be easy to miss the lesson, or have it work less effectively than for those who were in the processes of gaining those understandings and functions.
Therefore, pay attention to the outer work and lessons to evaluate the Teaching, but also remember from your own experiences how to learn a skill going step by step. You will find some parallels.
Will there be some underlying qualities, attributes, or approaches that are constant and present in the approach of Teachers? Yes. These tend more toward their Real personalities and things they emphasize. You will find some common qualities in those Real Teachers.
First, they tend to be freeing rather than controlling. If a setting, teaching, or person wants to control you - it is usually time to go. The Teacher will be a person of joy. If he is sour, sad, morose, complaining, and negative, it is likely he is a fraud. Again, the outer appearances can be misleading, but by careful observation you should be able to determine if it is a mask put on for a purpose or that person's active personality.
There should be a feeling of joy, peace, and love through the teacher. It should be apparent and inspirational. The heart should feel all encompassing. Giving, rather than taking is the rule. The Teacher will never depend upon the student for support - money, ego, gratification, status, or otherwise. No matter how much is given to him, nor how much he accepts, he will not accept it for personal gain.
The Teacher will speak from the heart. He will not bow to niceties when they are not warranted, nor will he offend and be harsh when kindness or consideration is needed. He will shield what needs shielding, hide something that needs hiding, and be stridently outspoken and blunt when that is needed.
In speaking from the heart, the Teacher becomes the pipe or flute. This only comes from long reliance on the intuition and Guidance that eventually becomes part of his process and he part of it. In this manner he is able to express whatever is needed at the given time.
The same is true of his level of consciousness. It will change and both go to and include the level(s) that are needed at the time to convey what is appropriate. Part of the work of the Teacher is to have developed that function. It comes from trial and error, until that reliance and trust is to the greater Spirit of Guidance, and it has grown from "permission" to allow it to manifest as and through oneself until it is total, unassuming, and natural. This is part of a base the Teacher needs to function. What starts as intuitive and seemingly external guidance and inflow, develops with attunement and a shift of identification to being a part of oneself.
The Teacher will not think of himself as anything special. Rather he will be aware of how small the person is in comparison to all that is and that can be. He will be aware of how special everything and every one is - not only as "others", but also as himself.
He would not cause harm to another, as much as he would not harm himself. But he will remove the splinter from his body if it should not be there. He will not exceed his limits of authority or position, nor impose himself on someone's free will. He will try to assist one to expand ones own scope.
He will not have anger or bitter words outside of himself. That is, he may express what seems like those feelings, but they will be controlled, not ruling - it will be appropriate. He will be sincere; will have a sense of humor, and not take himself too seriously.
He will assist rather than do, and can take the position of the lowest without feeling put upon. He will accept that which is provided and that which comes as sufficient, embracing each thankfully and equally. He will be a friend, a guide, and an assistant.
These are some of the qualities to see and feel in the Teacher. If they are missing, you would be wise to look elsewhere; or certainly consider why you do not see them. If they show up also in the disciples or students, you may feel you are probably in the right place.