One of my friend was wondering how does Google monitor link sales. If, let's say, one webmaster makes all these transactions in Gmail, will Google find out? Or what other ways does it use to find out about these sales?
It can track whether the sites you link to are unrelated or spammy and it can search for suspect strings.
Well that's the obvious answer but Google can come up with better things than just this, like the first idea I said. Google would look for links to crappy websites or unrelated websites since if you are linking to them, you are either a SERPs spammer or selling links.
Perhaps they look for places where there are a whole sequence of links without any intervening 'normal' text, and/or where the links are all related to different subjects?
Well I suppose nothing's impossible but I really doubt it, there are much better ways to identify them. I would guess there would also be privacy/legal issues if they were acting on the content of mail sent.
they have more than one criteria and they are secret. i think the criterias are * labeling with "sponsors" , "ads" * using sentences like "buy a link" * link places . most of the paid links are at the footer of the pages. * unrelated links