Remember all that cheap content you put on your blog because you thought you had to post several times a week? You know – the stuff that made little sense, and if a potential customer saw it they would think you never made it past the 4th grade…
Google has updated the Webmaster Guidelines to include that under “Content Spam”.

But before you panic – note that it says “low quality” not “all”.  Take a good look at those guest posts and ask yourself if it Filler or Killer.

https://www.seroundtable.com/google-low-quality-guest-blogging-considered-content-spam-19001.html

And the “Told You So” link from a year ago: http://bit.ly/blogfiller

Google Guidelines Update: Low Quality Guest Blogging Considered Content Spam