Negative SEO is a moneymaker, like negative reviews of businesses used to help improve a site’s rankings as angry customers left links.
Whether negative SEO works or not, the perception is that it does work. The reason? Google has stated that they will penalize “”unnatural links”” and the websites that have them.
This has led to an increase in spam across the web as negative SEO companies either extort innocent businesses, or businesses hire a negative SEO company to try to ruin a competitor.
Does it work? Who cares. Penguin and manual penalties have given the impression that it can work, and people think they can exploit the fear/reality by increasing the number of spam links across the web.