It may be useful to review some of related legislation about accessibility:
Voluntary Product Accessibility Templates (VPAT) outline how well a provider complies with section 508 requirements. VPATS are not universally mandatory for private sector providers, but some buyers do require them before a purchase is made. It’s important to keep in mind though that a VPAT does not necessarily guarantee that a website is accessible, but you can get a sense for a websites accessibility strengths and deficiencies.