Using only the guidelines above will not necessarily result in a fully accessible website, but it is a good starting point. Finally, the result should be validated by comparing it to the appropriate version of WCAG. At Dropsolid, we do a comprehensive audit of your website, using our accessibility knowledge and automated test suites like Axe. When we validate or audit a site, the check is always done by someone who has been trained in accessibility (e.g. AnySurfer).
It is important to note that test suites are not a comprehensive solution, therefore manual checks are necessary. Context is important when applying the guidelines and an automated system cannot (yet) estimate this. So certain expertise is required to apply the rules correctly and to set the right priorities.
If you want to go a step further, it is possible to have audits and reports prepared by individuals who have received specialized training, for example through the IAAP (International Association of Accessibility Professionals). A site that is tested by them (and passes) will then receive a certificate.
In Belgium, there are a number of organizations that have these kinds of professionals, the best known being Eleven Ways and AnySurfer. For example, if someone from AnySurfer positively evaluates your website, you can put a label in the footer of your site that lets everyone know that your site was tested by them. This is not a must to be accessible, but an external validation sometimes provides extra confidence.