Leaving aside master's slightly disturbing quest for death skills and adding to Chen Zen's orginal post:
When visiting a school also check out the senior students in the class. Are they respectful to the teacher, each other and the junior students. Are they keen to help you through those difficult early days or are they more interested in showing off their own skills? Do they inspire you to want to gain their knowledge. Senior students are a reflection of their teacher and should exhibit self discipline, loyalty and commitment. Ideally they should be approachable and provide a bridge between instructor and junior student - in the traditional Chinese set up the school was like a family with the senior students acting as elder brothers or sisters.
You should also check to see if the instructors teaching style is one you can get along with. Some instructors are rigid disciplinarians which suit some people not others, some are more open and chatty etc. Can the instructor talk the talk and walk the walk? Can he explain the concepts in a way that make sense to you as well as demonstrate them effectively? If so you have hit the motherlode.
Good luck and happy hunting.