Reviewing the results of the vendor's independent control reports is the best way to assess the risk associated with using a SaaS vendor because it provides an objective and reliable evaluation of the vendor's security controls and practices. Independent control reports, such as SOC 2 or ISO 27001, are conducted by third-party auditors who verify the vendor's compliance with industry standards and best practices. These reports can help the customer identify any gaps or weaknesses in the vendor's security posture and determine the level of assurance and trust they can place on the vendor.
Verifying that information security requirements are included in the contract is a good practice, but it does not provide sufficient assurance that the vendor is actually meeting those requirements. The contract may also have limitations or exclusions that reduce the customer's rights or remedies in case of a breach or incident.
Requesting customer references from the vendor is not a reliable way to assess the risk associated with using a SaaS vendor because the vendor may only provide positive or biased references that do not reflect the true experience or satisfaction of the customers. Customer references may also not have the same security needs or expectations as the customer who is conducting the assessment.
Requiring vendors to complete information security questionnaires is a useful way to gather information about the vendor's security policies and procedures, but it does not provide enough evidence or verification that the vendor is actually implementing and maintaining those policies and procedures. Information security questionnaires are also subject to the vendor's self-reporting and interpretation, which may not be accurate or consistent. References =
* CISM Review Manual 15th Edition, page 144
* SaaS Security Risk and Challenges - ISACA1
* SaaS Security Checklist & Assessment Questionnaire | LeanIX2
* Risk Assessment Guide for Microsoft Cloud3

The primary purpose of identifying vulnerabilities is to remediate them before they can be exploited by malicious actors. While risk reporting and prioritization are part of the overall process, the most immediate goal is remediation.
"Vulnerability assessments identify weaknesses that need to be addressed to reduce risk to acceptable levels and prevent potential exploits."
- CISM Review Manual 15th Edition, Chapter 2: Risk Management, Section: Risk Assessment and Analysis This aligns with ISACA's official practice questions, where vulnerability identification directly aims to prevent exploitation.

Business assets are the resources that enable the organization to achieve its objectives and create value.
Identifying the business assets to be secured is the most important step in developing an effective information security strategy, as it helps to align the security goals with the business goals, prioritize the security efforts and resources, and define the scope and boundaries of the security program. (From CISM Review Manual
15th Edition)
References: CISM Review Manual 15th Edition, page 27, section 1.2.1.

Information owners are responsible for determining the initial recovery time objective (RTO) for their information assets and processes, as they are the ones who understand the business requirements and impact of a disruption. An external consultant may assist in conducting the business impact analysis (BIA), but does not have the authority to decide the RTO. An information security manager may provide input on the security aspects of the RTO, but does not have the business perspective to determine the RTO. A business continuity coordinator may facilitate the BIA process and ensure the alignment of the RTO with the business continuity plan, but does not have the ownership of the information assets and processes. References = CISM Review Manual 15th Edition, page 202.
When performing a business impact analysis (BIA), it is the responsibility of the business continuity coordinator to determine the initial recovery time objective (RTO). The RTO is a critical component of the BIA and should be determined in cooperation with the information owners. The RTO should reflect the maximum tolerable period of disruption (MTPD) and should be used to guide the development of the recovery strategy.