Google's John Mueller said in a Google Webmaster Help thread that making quality links is against their Google webmaster guidelines. He said "if *you're* making quality links to your site, then that would be considered against our webmaster guidelines, and by that, those links would definitely not be considered "quality"."
Google wants natural links, links you do not go out specifically and "make." If you make links than by definition, those links are not natural and thus against Google's guidelines.
Of course, Google's link building guidelines have evolved over the years and Google is way more strict about what is classified as a natural link versus what is not.
So be super careful when you hire an SEO who does link building.
Forum discussion at Google Webmaster Help.
Update: More from John on this later today:
What's the difference between those that you legitimately make, and those that you make undeservedly, @ingobousa ? (not trying to be snarky; I want to understand where you see the difference & if we can make things clearer)
— 🍌 John 🍌 (@JohnMu) October 3, 2018
