I have been working with someone online. (Flame RavenHawk) I saw and read her posts for many months before she offered me help. I greatly respect her and her opinions and she is not quick to judge. She also doesnt belittle my beliefs where they differ with hers. This is the kind of person who makes a good teacher.
A bad teacher would be the opposite of this. Someone who is teaching for reasons other than knowledge. Someone who is teaching to gain power over others or to make themselves feel important. Someone who forces their beliefs on their students or will not accept their students beliefs as being just as valid as their own... Someone who is inflexible, just to name a few.