Depending on where you live, laws will vary. In the United States, not every state requires registration, or certification for Martial Art Schools in general. If your complaint is related to an alleged illegal, or fraudulant act, then I suggest you contact the local police, or go directly to the prosecutor's office and file a complaint. The prosecutor will decide if there is sufficient evidence to press criminal charges. If your complaint is more of a "dissatisfied customer" type, then you could try following the chain of command for that instructor / school (if there is one). Provided the owner of the Dojang (school) is not an independant individual without proper credentials or certification, he or she should have a senior master and Grandmaster as an overseer. You could check to see what organizations the school is affiliated with (IE: WTF - "World Taekwondo Federation," ITF "International Taekwondo Federation," USTU - "United States Taekwondo Union," ATA - "American Taekwondo Association," etc.). A formal written complaint sent to the president of the organization might result in disciplinary action, or revocation of certification. However, it has been my experience with the Korean culture, and the Taekwondo community in particular, that they will tend to cover for each other, expecially if it is a high ranking Korean in charge of the school. Still, making a written complaint can cause some concern and ripples in the organization. Perhaps the best option you have available is to contact the Better Business Bureau. Bad comments to them can sometimes affect the instructor more than internal discipline. Customers should check with the B.B.B. before joining a school to see if there have been any complaints in the past. A letter to the editor of the local paper might bring about some results as well. Just be sure you have your facts straight, and don't make any unsubstantiated accusations that you can not prove.