Black hat SEO technique is illegal.They are not good to use. It does not follow the rules and regulation of google. My suggestion is never to use black hat SEO technique for your website. It used to fool google and also users.

Are you aware of what Black Hat SEO is all about and what harm it can cause your online presence, Did you know that it can permanently get your website banned on the major search engines. Black hat SEO really doesn't pay off. The result is poor user experience because of the black hat SEO techniques used by the Webmaster to fool the search engines into believing the page was relevant to the search.

Here are some common Black hat techniques:
Keyword Stuffing
Hidden Text
Doorway Pages

All of these methods can get your site banned from the search engines, so when outsourcing SEO work,
check over your website to ensure none of these tactics are being used on your website.

Black Hat SEO is an unethical SEO technique which will surely bring your website to top position but will also lead your website to be penalized or even banned.

Black hat seo does not follow guide line of search engine.

Black hat seo techniques are

Doorway pages
Keyword stuffing
Link Farming
Hidden Links
Duplicate content