I have been involved in a variety of martial arts, on and off, for many years of my life. I finally found myself in a place to stick with a program for an extended time, and am approaching a second-degree black belt test in December 2020 for Krav Maga.
As I have advanced, I have had folks ask from time to time whether I could teach them. The answer has been "No." While I would enjoy sharing what I have learned, there are good reasons for both myself and a potential student that I will explain below. I am going to group things to consider into two categories: qualifications and compatibility. While there are exceptions to many of the points below, this is a good starting point for choosing an instructor and school.
Qualifications
Second Degree
Simply stepping into a dojo to begin training sets a person apart from the majority of others. By doing so, such a person has expressed a desire to become better than they are, and an interest in the martial arts. A number of these people will make the commitment necessary to achieve a black belt, and then having reached that goal, call it good and stop. This is a great personal achievement, but is distinct from those with the passion and drive to recognize that the best is still to come, and who continue to push themselves. With this in mind, it is recognized in many arts that a head instructor should have attained at least a second degree black belt. While junior instructors may hold first degree, or in some cases advanced ranks below black belt, they should be selected as outstanding and capable of teaching under the supervision and direction of a more advanced head instructor.
Personally, I like to find someone who has also ranked in multiple styles, and is always learning and seeking ways to improve themselves.
I am not yet second-degree, though I am nearly there!
Teaching Skills
Knowing how to defend yourself, and knowing how to communicate that knowledge are two very different things. An instructor should be trained and certified, specifically for the age and materials involved in the training. They should also continue their own training. This ensures that what is being taught is technically correct, effective, and up-to-date with recent advances in the art, and that it is taught in a manner that is beneficial and appropriate for the student to learn properly. It also ensures that the instructor is confident and comfortable in front of students, which is essential!
I am taking training that will help me teach, but am not certified, and only assist the instructors occasionally at this time. I am not comfortable solo in front of a group.
Philosophy
An instructor should be committed to the principles of the black belt, not just the knowledge. Knowing techniques to defeat an opponent is just one part of martial arts. Knowing when to apply that knowledge - and when not to - is just as important. There are six principles we build on beyond the technical knowledge - modesty, courtesy, self-control, integrity, perseverance, and indomitable spirit.
Compatibility
Passion
An instructor cannot be better than their desire to teach. Someone who wants to teach will already be doing it or be actively working towards it. Asking someone who does not teach already, to wedge it into their 'free' time when it is not their primary career, cannot have the same outcome as going with an established school, with instructors who have trained and dedicated their time to it, and which uses an established curriculum.
I have a different career, family, etc. and cannot dedicate the time to teaching that a student deserves. I enjoy martial arts tremendously, but not to the point of making it a new career in my mid 40's.
Cost
An instructor has invested considerable finances and many years of their life reaching the point where they are ready to teach. While it is important to find a school that is affordable, it is also important to recognize the value of what you are seeking. Do not cheapen an instructor's value, investments, achievements and time by asking them to teach you for free or below the normal cost in your area. Remember the 'integrity' part of the principles above? Once you pay them, it becomes taxable. Taxable also means opening an enormous can of worms, with respect to insurance, facilities, equipment and much more. Teaching martial arts properly, therefore, is not only a passion, but is also a business in every sense.
I could not possibly manage a small business on the side of everything else in my life right now, especially at a price that would be affordable. I have no economy of scale to offer.
Convenience
Location, location, location! You have heard that before. Dedicating time to learning martial arts means travel time, too. Your dojo needs to be located close enough that you are willing to travel there multiple times a week. A dedicated facility is important for safety, cleanliness, and suitability for training overall.
I have neither the facilities, nor the money to rent suitable facilities, nor the time to drive far for teaching.
Atmosphere
Lastly, the atmosphere needs to be comfortable and conducive to learning. Training should be enjoyable, motivational, encouraging, and involve personal interaction both with the instructors and other students. It is far more enjoyable to learn with peers at your level than to learn solo. The friendships that can be developed at a school, the bonds formed by blood, sweat, and tears - those outlast the training and have a value all on their own.
I do not run a school and cannot provide the benefits that come from learning in a class of peers.
In summary, while we'd all love to grow up with our own Mr. Miyagi nearby, that's just not the way things work ordinarily. In the vast majority of cases, a school will be a better choice than asking an individual to teach you. Choose a school carefully, ensure that ranks are earned and not bought or given, and put in the time and work necessary to achieve your goals! Good luck!