Quality control in finance.
Generally, quality control is a wide concept. If you shall buy a used car, you may rely on the person or the company from which you buy the car. Or you may bring with you your friend that is a car mechanic. If you are an investor that wants to buy a company, you may rely on the company reports and the reports from the auditor. But as a professional, that is not enough. You do your own due dilligence.
Quality control and web development - a Semantic Web.
Related to web development the quality of a web page is about well-formedness, validity, usability, accessibilty and design. Ideally, the page (content) shall be available independent of the media it is presented on. Content shall be available in screen readers and and in a browser on your mobile phone. But first and foremost it is about content and the quality of the information available on the Internet.
The paradox is that this (these) site(s) and more specifically this page is not well-formed and for that reason not valid. The reason is obvious. Since this site is ad driven, we have to import code as is from third parties. The consequence of changing the code can be that the link to the merchant is broken. Sometimes you have to choose between two evils and choose the lesser. The lesser is for us an unbroken link. But if you do not use code from third parties, you should make well-formed and valid code from the start. Nest tags properly and close them. Make the code XHTML, that is more generally, XML well-formed.