The past several months have  afforded several high-profile examples of how search engine  optimization, or SEO, should not be done. Last fall it was DecorMyEyes and the case of the abusive business 
proprietor, and just recently it was JCPenney and the case of the short-lived black hat success.
Such stories are by no means the only ones out there, of  course--they've just drawn more publicity than most. Either way,  examples like these are a rich source of instruction for the rest of us  and a good reminder that in SEO--as in so many aspects of life--there's a  right way to do things, and there are wrong ones.
        Want to improve your company's search rankings? Then make sure you don't try to play any of these dirty SEO tricks.        
1. Cloaking Your Content        The No. 1 top offending SEO technique, according to both SEO software firm 
SEOmoz and 
Google's own guidelines,  is to design your Website so that search engines see one thing while  human visitors see another. This is commonly called "cloaking," and it's  generally considered the dirtiest trick there is.
        Car maker BMW kindly provided a vivid illustration of this  technique a few years back, as well as what happens to those who try it.  Specifically, it was discovered that BMW's German Website was using  what are called "doorway pages,"  or text-heavy pages sprinkled with select 
keywords, to attract the  attention of Google's indexing system. The particular search term it  focused on was "used cars."        

        So, when users searching for "used cars" found the BMW site at the  top of Google's rankings, they were naturally tempted to click on it.  What happened then, however, was that a JavaScript redirect would send  them directly to BMW's main page, on which 
used vehicles featured  minimally if at all.
        BMW's reward for its cloaking efforts? Google unceremoniously  kicked the BMW site out of its index, as Google engineer Matt Cutts  explained in a blog post from 2006.
        2. Acquiring Links from Brokers, Sellers or Exchanges         The second worst dirty trick, according to SEOmoz, as well as one  apparently employed by both DecorMyEyes and JCPenney, is to pay a link  broker or participate in other link schemes so as to get numerous links to your site from all across the Web.
        The reason this trick is tempting is that Google's page ranking  system factors in the number of links pointing to a page when it tries  to evaluate that page's importance. It's also tempting because it can  work well--at least in the short term, as JCPenney recently  demonstrated.
        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.
        In response to the case, however, Google says it has since tweaked its algorithms,  though it didn't explain specifically how. My assumption is that the  overall sentiment of a site's reviews are now a factor. So, lest anyone  be tempted, this is not a sustainable strategy, nor a smart one.        
6. Automatic Queries        If you're like most Website owners, you wonder how your pages rank  on various keywords at any given moment in time. Lo and behold, there  are even tools that will perform automatic queries for you, to find out  the truth from Google itself.
        The only problem is, Google doesn't like that at all. Tools such as WebPosition Gold, it asserts, "consume computing resources and violate our Terms of Service." Better avoid them.
        There are other dirty SEO tricks out there, to be sure, but these are some of the worst ones. If you handle your company's SEO  yourself, make sure you don't stray into these dangerous waters. If  someone else handles 
SEO for you, manage them carefully so none of these  slip by.