I can only answer the question in the context of one program, the marine stewardship program. They have an accreditation body independent from the Marine Stewardship Council, and it accredits certifying bodies according to a set of rules.
There are other certifying organizations, such as the responsible fisheries certification program which Kevin alluded to earlier in his opening remarks, that use the ISO process for accrediting. The ISO process has an accrediting body that accredits those who do the actual work under ISO, whether it's certification or otherwise.
There are different types of accrediting bodies out there that accredit firms to do this kind of assessment work.