Page 9: "Assessments, also known as audits, are one of several methods we use to measure compliance with our requirements. Assessments — conducted by independent, third-party auditors — provide a snapshot of a supplier’s performance."

There is an additional statement continuing the comment above:

"...and listening directly to hundreds of thousands of supplier employees about their workplace experiences" --> indicating the direct method of auditing (i.e., on-site/in person)

The excerpt below suggests that Apple also conducts its own on-site visits; however, it is not clearly stated in the statement:

p.9: In 2022, investigations and more than 200 surprise assessments — where the supplier facility was given zero advance notice of our arrival — were conducted in the United States, China mainland, India, Japan, South Korea, Taiwan, and Vietnam

More thrid-party assessment:

p.9: In addition to third-party Supplier Code of Conduct assessments, we require many of our suppliers to also undergo the RBA’s Validated Assessment Program (“VAP”), a facility-wide third-party assessment widely used by the industry. A total of 98 RBA VAP assessments were completed in 2022 at Apple supplier sites.