Search engine optimization (SEO) is the process of improving the quality of traffic to a web site from search engines results. There are two types of SEO technique: Black SEO and White SEO techniques.
But here we are discussing about various commonly used Black Hat SEO techniques:
Invisible text: This text is to be read by search engine spiders. It is often white text on a white background, stuffed with keywords.
Link Farming: It happens with no regard for relevancy when a group of websites hyperlink to one another. This can be done manually, but is mostly done through software designed.
Existing Client Interviews: you must actually interview 1-3 clients, not only to verify the results, but to gauge the ranking the client gives to the SEM. Don’t ask yes or no questions for SEM question. You will not get the information you need. You ask questions that require thought and listen, not only to what they say, but also how they say it.
Keyword Stuffing: This occurs when a block of text is filled only with keywords. When an SEO company generates a copy for your website, take a look at the keyword density. Because your copy should be comfortable and natural to read, not full of awkwardly keywords.
Deep Results/ Live Results: You must see live and “deep” results for existing clients when you are interviewing an Internet Marketing Company. Deep Results is the high ranking for many keywords for the same client. Then for other clients, get the same quality results and verify them live right in front of you from Google searches. Live results is simply going to Google, entering a keyword and verifying first page results for one of your clients. Also verify that the client is actually a client by seeing the Internet Marketing Company’s name on the home page’s footer.
Fake Pages: Fake Pages is also called as Doorway pages that exist only for search engine spiders. They are never to be seen by the site’s user. They are often fake articles, filled with nonsense text.
So, Black Hat SEO is simply not SEO just as spam email. The sources of these techniques are just trying to take advantage of the unaware.