Thanks for the comment polyfiber, for some strange reason there are a lot of people in aviation who think that holding an instructors rating is somehow an indication that the holder of said certificate is guaranteed to be a good teacher.
Having been in the flying instruction business since 1957 I have met many licensed flight instructors who have difficulty tying their shoes but somehow passed the flight instructors course. So much for using the possession of a flight instructors rating as a benchmark of high quality of teaching skills.
For the past few decades I have owned and operated an advanced flight training business and have done very well financially and customer wise without having held a valid flight instructors rating.....in fact I let mine lapse in 1965 and never saw any need to renew it.