Six Sigma has been developed decades ago and fine-tuned by many companies since then. However, there is no ISO standard or something similar guiding the deployment or regulating the certification of the key players, Green Belts or Black Belts. There is only one key requirement that helps distinguish between success and failure: business results.
The easiest task in the journey to deploying Six Sigma or similarly Lean Six Sigma is the training of Green Belts and Black Belts. Many training companies have discovered this gold mine and produce hundreds of Belts every year. For small money, nearly everyone can attend twenty 3-hour evening sessions led by trainers who have hardly run any projects to become a Green Belt including certificate. Taking this certificate, attaching it to the CV and going for the next job application is a question of days.