Conducting third-party security audits is the most effective way to assess vendors' adherence to security standards. These audits often include an in-depth analysis of the vendors' security policies, practices, and controls. This can provide an objective and comprehensive overview of the vendors' security posture and compliance with relevant standards. Reviewing the vendors' privacy policies is important but may not offer a complete picture of their security practices. Examining product data sheets only provides information about the products and not the vendors' security standards. Comparing SLAs can showcase the guaranteed performance and availability, but it does not directly address security compliance.