1. Reciprocal link request pages.
3. Outdated copyright date or last modified date visible on the pages.
4. Error pages that don’t send 404 headers or send content regardless of the page requested/query string entered.
5. Massive numbers of incoming links from link farms.
6. dead/404ing links.
7. High link churn.
8. No published contact address, email address or phone number.
9. A high bounce rate (surfers clicking back on their browser and choosing another search result).
10. Too much duplicate content.
11. Whois info for the domain which is the same as other domains previously penalized or banned. (Could also be true of adsense publisher/affiliate ID’s and other identifiable footprints)
12. Use of/links to affiliate programs that are known scams
13. Domains previously used for spam or that are blacklisted.
14. Stagnation (Site never changes)
15. Excessively long URI’s/URL’s (query strings or folder and file names)
16. A high percentage of affiliate links vs regular outbound links.
17. No / very few outbound links.
18. No / very few inbound links.
19. All inbound links are to homepage only
20. Outbound links to questionable/spammy/crap sites.
21. Profanity or explicitly adult language on a non-adult site.
22. Too many spelling errors.
23. Contains unrelated subjects (ex: a site that reviews toys and tries to sell insurance or cock hardening pills).
24. Lack of interest from social bookmarking sites.
25. MySQL or PHP errors in the pages
Don’t follow above bad SEO practices, says San Diego SEO expert Ryan Christopher