Matt, the disavow tool is most certainly incontrovertible proof that negative SEO works. Why? Because whether a "spammy" link has been created by a website's ow

Matt, the disavow tool is most certainly incontrovertible proof that negative SEO works. Why? Because whether a "spammy" link has been created by a website's own misplaced SEO efforts or through that of a third party which wishes them ill, the effects are the same: a negative effect in ranking. We know from google that "spammy links" can and do indeed negatively effect rankings - this is why google has provided website owners the ability to 'clean up their act' in the first place But it does not matter who created the link, the effect is the same, hence, negative SEO works.