Black hat techniques means to redirect users in unethical way. For a small time period it brings a good result but its not good for long time period.So generally one should try to avoid this.
blackhat SEO is the process of manipulating the search engine rankings in an unethical manner that are against the search engines TOS... doing those kinds of strategies can have a risk, a site may suffer to some consequences or may lead to ban and penalties.
I am also curious with this technique. But now I know...
Black hat SEO techniques might have some short term positive effect, the long term implications can be disastrous for your website and in turn your business.
Some techniques are Link Farming and Doorway or Gateway pages .
Most of BlackHat marketing is trashy or unethical. Then some of it is borderline. Just be careful with it. You could lose your google adwords account, youtube account, etc.