VW uses both self reporting and independently conducted audits to ensure supplier compliance with company policies and local laws. The self reporting method relies on standardised self-assessment questionnaire (SAQ) to measure a supplier's S-Rating (Sustainability Rating) (Page 10). The information and documents provided in the SAQ are checked and validated by a service provider (Page 10). Since 2020, they have used a "service provider" to audit suppliers using AI (Page 12). So while its clear VW uses an independent auditor, they have not disclosed who.

Further, VW has made it clear they conduct on-site inspections, but have not clarified if they are self reporting or independent.