You did not indicate what you want to zero in on so here is a broad list of topics you would want to look for in a professional flight instructor. This list does not include everything of course:

1) motivates and challenges the student
2) informs the student of their progress
3) individualizes the lesson material to suit the student needs
4) gives credit to the student when they are successful
5) critiques student performance in a constructive manner
6) demonstrates consistency in their actions and behavior
7) admits errors when aware of them and tries to correct
8) demonstrates sincerity in purpose
9) accepts the student as they are in order to help them reach the goal
10) demonstrates professional standards of appearance, demeanor, and punctuality
11) does not distract the student from the goal
12) insures the safety of the student and adherance to regulations
13) uses clean language
14) strives for continual improvement in teaching skills
15) shows regard for the high cost of training and offers tips on how to reduce it

Does this help?