Google uses a patented learning machine techniques using real human to read your content and answer several question to see if your site passed their quality check list.
Here are the sample question they asks themselves to differentiate high from low quality.
1. Would you trust the information presented in this article?
2. Is this article written by an expert or enthusiast who knows the topic well, or is it more shallow in nature?
3. Does the site have duplicate, overlapping, or redundant articles on the same or similar topics with slightly different keyword variations?
4. Would you be comfortable giving your credit card information to this site?
5. Does this article have spelling, stylistic, or factual errors?
6. Are the topics driven by genuine interests of readers of the site, or does the site generate content by attempting to guess what might rank well in search engines?
7. Does the article provide original content or information, original reporting, original research, or original analysis?
8. Does the page provide substantial value when compared to other pages in search results?
9. How much quality control is done on content?
10. Does the article describe both sides of a story?
11. Is the site a recognized authority on its topic?
12. Is the content mass-produced by or outsourced to a large number of creators, or spread across a large network of sites, so that individual pages or sites don’t get as much attention or care?
13. Was the article edited well, or does it appear sloppy or hastily produced?
14. For a health related query, would you trust information from this site?
15. Would you recognize this site as an authoritative source when mentioned by name?
16. Does this article provide a complete or comprehensive description of the topic?
17. Does this article contain insightful analysis or interesting information that is beyond obvious?
18. Is this the sort of page you’d want to bookmark, share with a friend, or recommend?
19. Does this article have an excessive amount of ads that distract from or interfere with the main content?
20. Would you expect to see this article in a printed magazine, encyclopedia or book?
21. Are the articles short, unsubstantial, or otherwise lacking in helpful specifics?
22. Are the pages produced with great care and attention to detail vs. less attention to detail?
23. Would users complain when they see pages from this site?
These are the questions that Google asks real readers to decide whether your website is trustworthy or notable. These answers are collated and merged to their machine learning technique to discern whether the content of your site contains high quality information and trustworthy information. Some of these websites that are deemed to be trustworthy by Google gets the HTTPS or secure server website that means your website runs on a secure server and had been verified by Google.