A CRM audit inspects the system: fields, automation, permissions and data quality. A GTM diagnostic inspects the business through the system: how many deals convert, how long each stage takes, where hand-offs leak and what fixing each leak is worth. In a diagnostic, data quality shows up only where it breaks a number you care about.
That difference decides what you get at the end. An audit produces a cleanup list; a diagnostic produces a sequenced plan, with the CRM work ranked against the revenue it unlocks. Most companies need the diagnostic first, because it tells you which parts of the audit are worth doing at all.
Every claim above comes from work LeanScale published. These are the sources.