SEO kingpin Bruce Clay has published an SEO Code Of Ethics, but it’s pretty broad.
So what are all of the SEO bad guys using as black hat techniques? There are a few.
Ever go on craigslist and search for something, and in the results there are a few things that have nothing to do with what you searched for? This is likely because spammers inserted invisible text at the bottom of the listing so that their listings would come up more often. Invisible text is definitely a black hat technique, but this is also an example of keyword stuffing where keywords are either improperly used or overused on a page to try to deceive the search engine spiders of how much keyword relevance their page actually has. It is true that by strategically placing your keywords you have a chance of optimizing your content, but using the same keyword five hundred times in three paragraphs may be a little over the top. Spamdexing is similar, where certain phrases are repeated constantly on a page.
Another black hat technique that is very popular these days is using link farms to build backlinks. A company will promise to get your site 3-500 backlinks in a month, but how are they doing this? They’re using a network of irrelevant spam sites to back link to your page. These sites are likely already exposed by Google as being unimportant, and have received a pagerank of 0 for their efforts. Think this is damaging your sites chances of moving up the search result pages? Quite a bit, actually.
Text link ads are beneficial depending on what sites they are placed on, but I would highly recommend checking the page rank of any sites where your site will be backlinked from, as well as routinely monitoring what sites have you backlinked to make sure you’re not screwing up your chances with the search engines.
There are a few other methods of Black Hat techniques, such as Blog spamming, redirecting, comment spam, and more.
Spamming is lame. SEO is a 6-month and longer process because it takes a lot of hard work to build resources, backlinks, and optimized content for your site. So anyone promising quick results for a set amount of money is likely using one or all of these techniques, but it’s nothing but a quick fix that will damage your site’s reputation in the long run.