What evidence supports a marketing spend audit beyond invoices?

Invoices are only one part of the evidence trail. They show that a payment was requested and approved; they do not prove that the campaign delivered valid, useful, contract-compliant activity.

Useful evidence may include approved campaign briefs, contract terms, platform exports, invalid-traffic reports, media placement reports, lead files, consent records, CRM conversion data, duplicate checks, complaint logs, sales feedback, budget approvals, and management review minutes.

The auditor should connect payment approval to performance validation. For example, if a vendor bills for 18,000 leads, management should have some control that evaluates whether those leads came from approved sources, passed basic quality checks, and were reviewed before renewal or payment decisions.

The audit conclusion should distinguish:

• invoice approval control,
• vendor-performance control,
• data-quality control,
• privacy or consent control, and
• management-reporting control.

That distinction keeps the report from overstating assurance based on a clean accounts-payable sample.