How Can Google Distinguish Sold Links From Natural Links?

Interesting hypothesis, though in my opinion, it'd be difficult to implement a number of tests that would yield at least "workable" results. By "workable", I mean something that can be used by others, i.e. If someone could "accurately" know (at least "accurately" enough to a point where it becomes usable) if they can detect paid links or otherwise, then this person'd also know how to make paid links appear natural for the Google SERP algorithm)...

Then, in my opinion, they'd be missing out on a few hundred thousand or more because they initially need to set a well defined set of parameters for forms of payment that'd fall under unacceptable standards, that they'd again need to define another set of well defined parameters for. And, they'd need to perpetually keep on hiring more and more people just to keep at pace with the workaround solutions those link spammers and link sellers'd be perpetually testing out, implementing, monitoring and improving. So, in my opinion:

It'd be best for their business objectives to focus on other factors that can improve the accuracy of their SERP algorithm in providing their users with the most relevant, most timely and most popular results. They can in fact release placebo news about new code added to their SERP algorithm that can detect if a link is paid, just to confuse link spammers and throw them out of their game or link sellers and throw them out of their businesses. They can also publish these placebo messages through, just like link sellers and link spammers, behind-closed-door deals, so they can use reputable media outlets to publish this news for them, but then again:

I for one find it hard to believe that they'd be thinking of these things while they already have their hands full with a lot of other stuff, so again, in my opinion, they'd focus more on the other heuristic factors that make their SERP algorithm run as how they want it to, and I'm referring to "other heuristic factors" as factors which don't have that much of gray areas compared to code or even a manual system of sorts that could detect if a link is a paid one, based on a well defined set of acceptable and unacceptable payment methods...

Yes, but there is a technique of selling "editorial" links. Some people do this: they sell links within their articles to related sites.

Among links these are some of those that cost the most. But I hear that Google can detect these too...

I'm pretty sure they have thousands of staff checking sites manually.

They can't tell. They only guess. There is no do follow.

Buy your links in such a way that they cannot guess.

There are ways, but I aint saying. I sell tons of links.

One of the best ways google can tell a paid link, is if
someone blabs. They rely on that quite a bit.

The only natural links are with linkbait.

So many people in this thread are using do follow as if it
exists and means anything. It doesn't and it drives me crazy.
If you toss the word dofollow around, then what does that say
about the rest of what you are saying? Pure fantasy?

Paul