[hwang]

I don't know how they got to know about it. Maybe when you post about selling links in a forum and you include the site address and then when some google spies read about it, they will take action to penalize your site....Lol (just my guess)

But on a serious note, I think it's simple. Maybe sometimes certain people overdo it by putting 30 -40 links in a page, then they will get suspicious. Either way, a bunch of links at a site and none of them are related at all to the site content.