A 'clean audit' is used for government audits and means financially qualified plus adherence to laws and regulations. It's a variation or expanded definition of unqualified audit and is not used in non-state audits. 
There's no limit to the number of qualifications an auditor may report in one audit of an entity - not the 'one or two areas' he mentions. A qualified audit is not a 'watered down version' of unqualified because depending on the balance being qualified and the entity, it may have serious implications. It's not necessarily calamitous but receiving a qualification is a serious indictment on the concern's financial management. Imagine a bank receiving a qualification on its mandatory reserve balance? A qualification particularly of cash and cash reserves is serious.  He forgets disclaimer of opinion, arguably the worse opinion there is.
I've been out of accounting for years but I remember this much. Is Mantell writing from memory or is he still active in audit?