I was looking up some terms such as Roshi and JDPSN, and I found this on a very helpful page at the Urban Dharma site:
Firstly, a good teacher has made progress in attaining freedom from ignorance. This means the teacher has arrived at some understanding about the nature of existence, and is able to show a genuine compassion. You should not hear a teacher quoting from a New Age bookshelf.
Freedom from ignorance also means a sufficient grasp of the teachings to be able to answer your questions. In fact, the Buddha was very clear that all followers should test all his teachings against their experience. The Buddha very much encouraged all visitors to ask questions. You should be able to get straight answers to your questions. Do be respectful, do be truthful with yourself, do focus on what matters to you, but do not be shy to ask, even the same question over and over. And do listen closely to the answers you hear. A good teacher will find a way to give you an answer that speaks to you, at your level of understanding.
Secondly, a good teacher is largely free from greed and lust. How can you tell? One way is to stay sensitive to an undue focus on your generosity. Be cognizant that your generosity benefits the community rather than accruing to specific individuals. Also look for signs of attachment to things and to people. What might be some signs that there is some funny business going on? Perhaps the teacher lives a fine and comfortable lifestyle. Perhaps there are too many women around who praise the teacher excessively and uncritically.
Thirdly, a good teacher is advanced in developing freedom from anger. Such a teacher might have a “lightness” in style and would not be trapped in his own “likes” and “dislikes”, exhibiting kindness towards others, even very ignorant and difficult students. You would not find an authoritarian attitude where something is so because it’s written here or there, or because the Buddha said so. In fact, any display of anger for any reason is a seriously unwholesome act. So-called “skillful” anger is no different from plain anger; it is therefore a dangerous concept.