The most important thing to include in the vendor selection criteria when procuring security services from a third-party vendor is B. Alignment of the vendor’s business objectives with enterprise security goals. This is because the vendor should be able to understand and support the enterprise’s security vision, mission, strategy, and policies, and provide services that are consistent and compatible with them. The vendor should also be able to demonstrate how their services add value, reduce risk, and enhance the performance and maturity of the enterprise’s information security program. The alignment of the vendor’s business objectives with enterprise security goals can help to ensure a successful and long-term partnership, and avoid any conflicts, gaps, or issues that may arise from misalignment or divergence.

The vendor should be able to understand and support the enterprise’s security vision, mission, strategy, and policies, and provide services that are consistent and compatible with them. (From CISM Manual or related resources)

References = CISM Review Manual 15th Edition, Chapter 3, Section 3.2.1, page 1341; Third-Party Vendor Selection: If Done Right, It’s a Win-Win2; Vendor Selection Criteria: Key Factors in Procurement Success3