There are many SEO service providers who employ different techniques to "trick" search engines for ranking their pages up in the results pages for specific keywords. These are illegitimate means used for SEO rankings and include the use of doorway pages, and hidden text for duping a search engine rank a site high enough in the rankings. Because of this, those sites which use black-hat SEO tactics drop their rankings as fast as they climb up in the rankings.
Here are some of the tactics which are used in Black Hat SEO which are not at all recommended. Some tactics are simply modified from the below tactics and sometimes they do work, but one is risking getting their site blacklisted forever.
Keyword Stuffing is one of the most commonly abused forms related to SEO spam. The SEO vendor lists down a large number of instances of a particular keyword phrase that he needs to target with the hope that the search engines will parse the content as being relevant. The text generally reads badly and most of the stuffed content words will have small font size and listed at the bottom of the page.
The hidden text tactic includes text which is of the same font color as the background. Major search engines have the ability to detect the text while some webmasters create an image file in the same color and then set the image file as the background. Websites using the tactic are usually blacklisted.
There is a black hat SEO method which differs from search engine optimization techniques which is called cloaking. It is a method of presenting different information which a visitor will not be able to see. There are multiple methods used for cloaking which can dupe the search engines. It is possible that any of the competitors might see through what you are actually doing and might land you in trouble.
Doorway pages are those pages which are added to the website for targeting some specific keywords or phrases. They are not for visitors. There is no information in these pages. Injection of doorway pages are banned by all main search engines and any report of such a practice will make your website disappear along with the legitimate strategies and genuine content pages that you had on the site.
Redirecting is not a general black-hat tactic but can be brought in to help out doorway pages. Redirecting links send the visitor to pages where the actual content is, such as the homepage of the site.
Incoming links are extremely important for search engine positioning which also impacts the overall link popularity. This tactic is very difficult to detect from a user standpoint unless there are multiple pages in the topmost rankings of search engines which would create a doubt that something is fishy about the SEO tactics used on the site.When unfair tactics are being used, one can always report the competitor and it is a fair practice on your part. One can easily report spam pages and sites but make sure that your own site is good enough!