The web is full of links.
They are the ones that create the so-called "networks" so people and machines could browse from one page to the next, in order to gain more context about a given subject.
There are a lot of discussions regarding links, and how they should be obtained.
Some suggest that backlinks can only be earned and not given, and others say that people have the rights to receive backlink if they have the money and paid for it.
John Mueller from Google tried to clarify this in a video.
When he was asked:
"if I dofollow backlinks due to paying bloggers to write highly relevant review articles or paying for high-quality PR news articles, are they paid links that go against Google's guidelines?"
Mueller's short answer is "yes", it is against Google's guidelines.
Mueller said:
The problem here is because rel="dofollow" links will pass PageRank, and Google doesn't like that people are tricking its algorithms by commercializing backlinks.
Google has even warned webmasters and web owners if gaining links is their primary purpose.
Since any link with any attribute can pass traffic, Google wants websites to use the required attribute for each corresponding link.
This is why Google wants websites to use the rel="nofollow" attribute for outbound links, and in this case, the rel="sponsored" for paid links.
Using those attributes, the links won't pass any PageRank value to the target website. But the link can still help users and Google find the content, and indirectly promote the content.
In Google's perspective, that is the way to advertise.
Related: The Dos And Don'ts When You Are Building Backlinks
We're not that new at this.
— John (@JohnMu) January 18, 2021
It should be noted though, that paying for links is already a common practice on the web.
There are many websites and blogs out there that openly or discreetly provide ways for advertisers to sponsor them, and in return, will give them backlinks. The more respectable a website is, the more authoritative it is in the eyes of Google. Because of that fact, prices can vary, and become increasingly expensive to get backlinks from those websites.
And the price for links with the rel="dofollow" attribute is the most expensive among all attributes.
But the thing about this kind of transaction is that, it is often made through emails or direct/private messages. It can even be made through third-parties which connect advertisers and the bloggers. What this means, most if not all of the transactions are made behind Google's back.
One Twitter asked this, wondering how can Google know which of the links are paid.
"Conversation is done by email and nobody mention this on the site that buy links from here. Everything is done under the table," the Twitter user asked.
Mueller replied that Google is "not that new at this," suggesting that the search engine giant may know a thing or two (or more ways in which it doesn't want to share) to track those paid links, even when they were made behind its back.
Further reading: The Reasons Why Your Backlinks Aren't Helping Your Search Engine Rank