This isn’t as clear as it might seem at first glance!
Many people incorrectly believe that the word ‘paid’, suggests that paid links are only where someone has exchanged a currency based transaction, in order to receive a link. Although this is certainly one type of transaction which can be classified as a paid link, it most certainly isn’t as clear-cut as the phrase leads people to believe.
Like it or not, Google is the judge, jury & executioner when it comes to ultimately deciding what is and what isn’t a paid link. Therefore they’re allowed to write the definition:
Buying or selling links that pass PageRank. This includes exchanging money for links, or posts that contain links; exchanging goods or services for links; or sending someone a “free” product in exchange for them writing about it and including a link
Google have been warning webmasters against participating in links schemes since 2003, and later more specifically by Matt Cutts about buying and selling links. Whilst they might change the terminology from time-to-time, or clarify a particular type of paid link the message is pretty much the same as it has always been since the attribute nofollow was introduced.
Buying links where directly, or indirectly in against the Google Webmaster Guidelines and if you are found to be breaching them action can (and will) be taken against your website(s).
Google (other search engines as well) are getting better at identifying (what they deem to be) paid links by the day, so it’s more of a question of when, rather than if paid links will harm a website. The more obvious a paid link, the easier it is to identify by algorithms, and the more likely it will affect the organic search traffic of a website.
Different action may be taken against a site, depending on the nature and scale of the paid links discovered. If there are for example only a handful of links, which are determined to be paid by an algorithm, then these might maybe more likely to have the link authority removed with no further algorithmic, or manual action.
However if a quantity*, or particular type of paid links are found, which are deemed to need additional ‘quarantine measures’, then the algorithm(s) may apply an automatic adjustment to protect the quality of search engine’s results in order to protect their users from poor results. If the nature of the ‘link crime’ is deemed severe enough, then it may trigger a manual action by a member of the web-spam team.
There are many characteristics which can identify paid links. The below is by no means a definitive list, there any many more examples across the rest of this resource.
- Commercial anchor text – e.g. ‘buy blue widgets’
- Commercial landing pages – g. does it point to obviously optimised page to rank for a term
- Position on page – g. within context
- Page URL – e.g. domain.com/sponsor-links.php
- Content used on the page – g. “sponsored article”, “paid article”, “guest post”
- Location of the page – g. if the page is ‘hidden’ from the main navigation
- Number of links on a domain – g. is it a site-wide link
* The exact number is unknown and more than likely is based on complex equitation’s rather than a simplistic numeric number.