Companies that employ overly aggressive techniques can get their client websites banned from the search results. In 2005, the Wall Street Journal reported on a company, Traffic Power, which allegedly used high-risk techniques and failed to disclose those risks to its clients. Wired magazine reported that the same company sued blogger and SEO Aaron Wall for writing about the ban. Google's Matt Cutts later confirmed that Google did in fact ban Traffic Power and some of its clients.
Before starting an SEO project, site owners should carefully read through the webmaster guidelines that each search engines provides and follow recommended best practices. Not only will doing so help pages rank better, but failure to follow recommendation could result in the site being improperly indexed. Worse still, the site could be completely blacklisted from the search engine. Certain black hat SEO techniques, such as keyword stuffing, are considered to be the SEO equivalent of spamming, and search engines will penalize them.