A certification body is the independent organisation that audits your management system and issues the certificate. In the United States you will still hear the older term registrar, which means the same thing.
Accredited or not
Anyone can print a certificate. What makes one meaningful is that the certification body is itself accredited — in the US, most commonly by ANAB or IAS — against ISO/IEC 17021, the standard for bodies providing management system certification.
An unaccredited certificate is not necessarily fraudulent, but many customers and supplier programmes will not accept it, which usually defeats the purpose of getting certified. Check the accreditation mark and, if in doubt, look the body up in the accreditation body’s public directory.
What they can and cannot do
A certification body cannot consult on the management system it audits. That independence is a requirement, not a preference, and it explains why certification body guidance stops short of telling you how to build the system — they are structurally prohibited from doing so.
This is why organisations often work with a consultant to build the system and a certification body to audit it. The two roles cannot be filled by the same organisation.
Choosing one
Ask about their accreditation, their experience in your sector, auditor availability against your target date, and how they calculate audit days. Compare quotes against the published audit-time table rather than against each other.