Accessibility-focused user acceptance testing brings in actual people with disabilities, screen reader users, keyboard-only users, people with cognitive or motor disabilities, to complete real tasks on a product before it ships, surfacing usability friction that a technical WCAG audit alone may not catch, since technical conformance and genuine usability are related but not identical.
This kind of testing is considered the gold standard for accessibility validation precisely because it reflects how real users with a wide range of needs and assistive technology setups actually experience a product, rather than how a single expert auditor interprets the WCAG success criteria.