What are the benefits and dangers to a corporation from working with NGOs to conduct sustainability audits?

Why are CSR audits important? What are the benefits and dangers to a corporation from working with NGOs to conduct sustainability audits? As part of the due diligence involved in selecting partners, a major client asks you to demonstrate your CSR commitment before awarding a large contract to your company. How would you address your client’s request and what measurable data would you provide?