The approval process is largely a norm established in your project. One approach that can be taken is to approve 'known' organisations associated with the project based on your knowledge of the organisation's skills and competencies. For organisations that are not known to the project, a more rigorous process can be followed whereby moderators review the applicant certifying organisation's web site, ask to review their training course curricula, the training materials used by the organisation, or possibly even sit in on a training course conducted by the applicant to verify that they "know their stuff". Once the organisation has passed approval, the organisation owner and mangers will be able to proceed with setting up courses, conveners and so on using the management interface provided on the QGIS Certification Website.