A Search Engine Watch Forums thread tells a tale of what I see every now and then from an SEO. Basically, if you mess with an SEO, they can put up a page, optimize it for your name plus a negative keyword and ruin your reputation.
For example, let's say I bought a car from a local dealer and I was very upset with the whole process. I can create a web site or even post an entry on a blog with the title "Car Dealer Name Ripped Me Off." Typically, ranking well for a company name is easy, unless they are huge brands. But when it comes to a local guy or even a person's name, typically, it is easy.
SEOs can do this almost at any time and some may. Scary? Well, many jobs have their perks. :)
Forum discussion at Search Engine Watch Forums.