When considering the above for consideration in qualifying an auditor, one should bear in mind it really depends upon the intent of the auditor. This is to say, if you want to be an RAB Lead Auditor you are going to need more than if the intent is for internal auditing.
For the individual company, the important part is that you define your minimum requirements. In some companies it is as simple as having attended an internal auditing course. One of my clients sent their QA Manager to a Lead Auditor course. He then used my Guide files to train his own internal auditors. This passed muster in their ISO 9001:2000 audit recently. He has added a training audit where another qualified auditor observes the first audit the new auditor performs.
Education, Training & Experience
Candidates should demonstrate competence in clear and fluent oral and in written concepts and ideas
Knowledge and understanding of the standards, systems and/or procedures audited
Assessment techniques of questioning, evaluating and reporting
Audit management audit skills such as planning, organizing, communicating and directing
Candidates should have four years full-time workplace experience
ISO 19011 - Quality and Environmental Management Systems Auditing Forum Discussions