Why shouldn't you use it? Well, mostly because it's in direct violation of Google's Webmaster Guidelines, and it can get you severely punished, as JCPenney learned. If you participate in a link exchange program--whereby you link to a spam site in exchange for their links to you--the outbound links you install are also another factor that will negatively affect your rankings.
3. Duplicating Content
If a Website operator offers the same content on multiple pages, subdomains, or domains, it can result in extra traffic and higher rankings--or at least, so the thinking goes. Unfortunately, it's another violation of Google's Webmaster Guidelines, and it can get you kicked out of its index.
Other instances in which content sometimes gets duplicated include affiliate programs that offer little or no original content, auto-generated content that's packed with keywords but makes little sense to human visitors, and content "scraped" from legitimate sites and then modified minimally.
Not only will such techniques get you punished by Google, but they'll also turn away human visitors. Note that when content is duplicated legitimately, such as for printer-friendly versions of articles, there are ways to alert Google so it doesn't misunderstand.
4. Keyword Stuffing
The keywords used on any Web page are a major factor in that page's ranking, but it's a bad idea to use them indiscriminately or deceptively. That includes using too many of the keywords you're hoping to optimize on--thereby exceeding any kind of naturally plausible keyword density--and it also includes packing keywords in hidden text, different-color fonts and tiny type.
Once again, Google engineer Matt Cutts offered some additional explanation in a 2007 blog post, along with an illustration: Alex Chiu, whose Web page featuring "immortality devices" was at the time stuffed with irrelevant keywords. Guess what? Chiu didn't show up in Google's index. (Since then, it appears to be back, presumably because the keyword stuffing has been corrected.)
A useful test, as Google points out in its guidelines, is to ask, "Does this help my users? Would I do this if search engines didn't exist?"
5. Banking on Negative Reviews
Although it was disputed by at least one SEO expert, the owner of the DecorMyEyes site believed that the more negative reviews and comments his site got--and there were many, thanks to his atrocious customer service--the better the site's rankings, primarily as a function of all the extra links and traffic. For a time, too, his strategy worked pretty well, for whatever reason.
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