Bing: Never Seen A Case Where Negative SEO Was Attributed To Ranking Decline

Bing's spam fighter, Frédéric Dubut, said on Twitter "I haven't seen any case where a change in rankings would be provably attributable to negative SEO only." We know Google has mostly said that negative SEO doesn't really work with Google, although they have been a bit wishy-washy on that. Here is Bing kind of saying the same thing.