MOZ considers the following factors when calculating spam score
1. Low number of pages found
2. TLD correlated with spam domains
3. Domain name length
4. Domain name contains numerals
5. Google Font API Present. This domain does not use special fonts (e.g. Google Font API). Lacking this feature was common among spam sites we found.
6. Google Tag Manager. Google Tag Manager is almost never present on spam sites.
7. Doubleclick Present. The Doubleclick ad tag is almost never present on spam sites.
8. Phone Number Present. Spam sites rarely have real phone numbers present on their pages.
9. Links to LinkedIn. Almost no spam sites have an associated LinkedIn page, hence lacking this feature is correlated with spam.
10. Email Address Present. Email addresses are almost never present on spam sites.
11. Defaults to HTTPS. Few spam sites invest in SSL certificates; HTTPS is often a good trust signal.
12. Use of Meta Keywords. Pages that use the meta keywords tag are more likely to be spam than those that don't.
13. Visit Rank
14. Rel Canonical
15. Length of Title Element
16. Length of Meta Description
17. Length of Meta Keywords
18. Browser Icon. Spam sites rarely use a favicon; non-spam sites often do.
19. Facebook Pixel. The Facebook tracking pixel is almost never present on spam sites.
20. Number of External Outlinks
21. Number of Domains Linked-To
22. Ratio of External Links to Content
23. Vowels/Consonants in Domain Name
24. Hyphens in Domain Name
25. URL Length
26. Presence of Poison Words
27. Uses High CPC Anchor Text