Google uses humans to check and evaluate content quality. This is their guideline they provide for training purposes.
This is a big PDF that will take awhile to load – it belongs to Google and was published in July 2018; it can be found following this link if you don’t want to wait or deal with scrolling through pages. https://static.googleusercontent.com/media/www.google.com/en//insidesearch/howsearchworks/assets/searchqualityevaluatorguidelines.pdf
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