Search engine experts usually work within the guidelines provided by the search engines to achieve results, however some practices, known in the industry as Black Hat SEO, fall outside those guidelines. Although they may still be effective, there are reasons why they shouldn’t be used, and your site may be penalized if you are caught using them.
Some practices, such as influencing which page on your competitor’s domain ranks in the search engines, or re-using old links to achieve higher rankings, are up for debate as to the ethics involved and acceptance by the search engines. The methodology for the latter involves updating or redirecting old pages to new content, but once you are “found out” by Google, for instance, they may blacklist your entire domain.
The solution is to make sure that the content you provide is the same content that is represented to the search engines. If you change or update a web page to induce higher rankings, be sure that the content on that page is relevant to the original content on that page. No trickery, no black hat technique, and no penalties.