If you undertake black or gray hat techniques, you run a fair chance of having your site penalized in the search results. But even if you are not engaged in these techniques yourself, your site may be punished for associating with black hat purveyors. Hosting on a shared server or sharing the domain registration information with bad neighborhoods can lead to ranking problems, if not punishment. Certainly, linking to a bad neighborhood can lead to discipline. If you purchase a domain, you'll nearly always inherit any penalties or bans imposed on the prior version of the website.

There is a wide range of penalties and ranking filters that search engines impose, and a still-wider range of effects that those penalties produce. In diagnosing and correcting ranking problems, more than half the battle is about figuring out which penalty, if any, is imposed and for what violations. Ranking problems are easy to fix, but are arduous to diagnose with...