A good teacher will know as much about learning as they do about music. They will want to understand the material from the student's perspective and have guidance about the path that the student is on. They will enjoy teaching as much as they do playing.
I don't know exactly how you screen teachers for this, though if you're working with one for a while you can tell if they want to be doing it, and whether they understand from the student's perspective. I would ask them how they approach teaching, and what resources they use to make them a better teacher. If their answer is about their own playing, that would be a flag for me. If OTOH they say at least something about theories of learning then I would be encouraged. If they tell you they have a set curriculum, that could be a good thing if it fits where you are and your own learning process, but it could be a sign that they won't adjust to the student. If they do have music education training, I'd ask how they keep current (since their schooling) to see if they're open to new approaches vs. stuck in a single dogmatic approach.
I have had bass teachers who were very good players, but were not interested in the craft of teaching itself. Sometimes they are both, but not always. They should be skilled enough players to demonstrate whatever you're learning, of course, but being a good player alone is not sufficient.
This should go without saying, but if you take up lessons with a teacher, you should leave each lesson with a plan of what you will practice before the next lesson. It should be clear, and it should be related to your interests and appropriate for your skill level.