There are hundreds of anecdotal claims of negative SEO attacks that worked, but so far none that irrefutably prove it. Most of the people who claim negative SEO victimhood are either unwilling to share enough information to confirm it, or in many cases it turns out that much or all of the spam was self-inflicted.
Regardless of whether or not negative SEO works on anything other than an already link-spammed site, clear proof one way or the other would be a big step in reducing the amount of linkspam being generated by those who believe it works, and eliminate the nuisance of link monitoring and endless disavowing and removal of links that responsible, grown-up webmasters did not want or ask for.
of is seeking a volunteer site to try to prove or disprove once and for all the theory that a site other than your own can be knocked down by pointing a bunch of bad links at it.
Unfortunately, what we don’t have is a solid, compelling, public example that proves the risk and helps unite the industry and press to nudge Google into making changes.
KerCommunications.com has been that “volunteer” in the past, though nobody actually volunteered for it. For what its worth, the account of what happened and didn’t happen when Ker Communications was struck by a wave of idiocy is here: kercommunications.com/seo/negative-seo-reality-check/
(Spoiler Alert: Many spammy links, nothing significant happened to rankings or traffic that could not be attributed to a variety of other things)