JKA certificate
There are certain qualities that an instructor has to have and these are aquired by applying and if accepted attending seminars, coaching classes, instructor training and examinations.
Below is the JKA model of instructor certification, don't know how up to date it is but it can be used as an example.
Japan Karate Association (JKA)
http://www.jka.or.jp/english/about/dojo.html
JKA Authorized Instructor Certification
Class D instructor
Application Prerequisites
2nd Dan 20 years of age or older
Testing Location
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Authorized Function
Upon Certification Qualified to instruct at branch dojo or group
Class C instructor
Application Prerequisites
Min 3 months wait after receiving 3rd Dan
Class D Instructor Certification
Testing Location
Regional HQ
Authorized Function
Upon Certification Qualified to instruct and train at National (Prefecural) level
Class B instructor
Application Prerequisites
Min 3 months wait after receiving 4th Dan
Class C Instructor Certification
Testing Location
Tokyo JKA HQ
Authorized Function
Upon Certification Qualified to instruct and train at Regional level
Class A instructor
Application Prerequisites
Min 3 months wait after receiving 6th Dan
Class B Instructor Certification
Testing Location
Tokyo JKA HQ
Authorized Function
Upon Certification Qualified to instruct and train at International level
Qualified to instruct at International training sessions
.