Google has sent a reminder to publishers that they should not misuse content -- which could put publishers and authors at risk of being penalized. The post warns against publishing guest articles for the purpose of building links with the intent to manipulate Google search results.
Those who do are "spamming the algorithm," wrote one person commenting on the post, reminding contributors that the "safe way to strike an advertorial deal is to put rel="nofollow" on the outbound links."
Google's penalties often negatively impact overall site rankings. While Google does not discourage these types of articles in cases when they inform users, educate another site’s audience or bring awareness to a cause or a company, publishers that are posting the content need to take a close look and determine whether the content fits the audience.
Some factors among many that can violate Google's guidelines include stuffing keyword-rich links to sites in articles; publishing across many different sites or many articles on a few large, different sites; using or hiring article writers who are not knowledgeable about the topics they are writing on; and using the same or similar content across these articles.
For years, Google and Facebook have dealt with issues around spam post links in publishers' content. In 2013, Italian researchers Andrea Stroppa and Carlo De Michel led a group that uncovered price lists for posting third-party links to Facebook fan pages.
As for Google, "any links intended to manipulate PageRank or a site's ranking in Google search results may be considered part of a link scheme and a violation of Google’s Webmaster Guidelines. This includes any behavior that manipulates links to your site or outgoing links from your site."