Google's Promises to Punish for Selling Backlinks - Myth?

Today the whole community of webmasters is buzzing about Google's promises to change their policy and fight more effectively the tactics of selling backlinks.

I am not going to dispute about the morality of purchasing backlinks for SEO purposes, because this is a subject for another discussion. But let's try to answer a simple question...

Is Google Really Capable of Stopping Backlink Selling?

And this is a very good question. What Google offers to do right now is to report sites that are selling backlinks and they will find out some algo to fight it. Google is not saying how exactly they will penalize, but I think the wisest idea would be to simply not count backlinks (in terms of rank calculation) if the site is reported for backlink selling. This should make the purchase of links not interesting for webmasters and break the whole trend of buying links for the sake of SEO.

BUT...

How exactly can Google tell good links (real links) from bad links (paid links made for the sake of SEO)?

I personally know many super reputable webmasters' forums that sell backlinks. Even on home page. (!) Intermingled with real backlinks (!). And Google will not be able to invent some algo that will tell good links from the bad links for all sites if the good and bad links are coming together. Because all links look super natural.

So, if it's impossible to invent this algo, this means sites that sell backlinks in a wise way are out of threat. And Google will be catching only stupid link farms and greedy average sites that create piles of backlinks.

Most probably Google will make a big public punishment for some minors - and that's it. Big sites will be still selling the backlinks. And webmasters will be still buying the backlinks.

All this makes me think that it's highly possible that Google creates the buzz trying to threat naive webmasters and scare them away from buying links.

But there have been many examples when Google's promises have been to far from what they have managed to do in real life.

P.S. And, by the way, don't you think that all this fuss about purchasing backlinks is a good proof that Google can still be manipulated with backlinks? :)