There are many types of Google Manual Action penalties. There will always be a message in Google Search Console telling you in what way you are violating the Google Webmaster Guidelines. Google Search Console was previously known as Google Webmaster Tools. Manual actions almost always result in huge drops in Google search results. If you have a Google Manual Action you will often find that you are still ranking just fine in other search engines such as Bing, Yahoo, DuckDuckGo etc. Here are some common types of messages that you may see.
Pure Spam Google Manual Action
This is pretty much what it says. Most commonly is content that is automatically generated gibberish. This is not a link problem, but an on-page problem. Unless the problem is really severe, it is fairly easy to fix the problem. Changing the content to well-written content and submitting a Reconsideration Request should be sufficient.
The pure spam penalty can become more difficult when you have something like a forum. User-generated spam is hard to control and you may have to consider losing a large amount of content. The same goes for sites that are scraping content from all over the web.
Thin Content Penalties
Once again this is an on-page penalty and not a link based problem. This is sometimes not quite as you may think. Keyword stuffing is more to blame than user-generated gibberish, cloaking, scraping, sneaky redirects, etc. This is a difficult manual action to fix and can involve editing large amounts of content.
Hacked Site Content
This is an old school technique typically used to create landing pages for multiple locations. For example
'best plumber in <every state in the US>'. This worked great for many years, but now you are likely to get hit with a manual action. Fixing this is just a matter of deleting all the doorway pages and sending a reconsideration request. A link audit may still be a good idea, because it’s possible that some of the doorway pages may have undesirable links. Even if they are linking to a dead page, we still suggest adding them to the disavow file.
Twenty years ago this was a common SEO trick to stuff keywords into the bottom of a web page with, for example, black text on a black background. This technique stopped working before the turn of the century. Since then webmasters have been hiding text using CSS and other more programmatical techniques. Google is, of course, one step ahead of the game and are more than happy to hand out penalties for such violations.
Unnatural Inbound Links
This is our specialty at Link Detective. Read more about unnatural links here.