Tom Hespos writes:

There’s good SEO and there’s bad SEO. Good SEO follows the rules and minimizes the risk of being delisted while increasing relevance to search terms germane to a marketer’s business. Bad SEO uses seedy tricks to elevate listings.

Tom’s right but there really are no rules. The line between right and wrong in the search engine marketing arena is grey. Smart marketers should avoid even getting close to the line or risk loosing their shirt. If you don’t know what you are doing get professional advice.