A Black Hat Method is the industry term for methods that are "shady" or on the "dark" side of Search Engine Optimization. They are loopholes in the Search Engine's website ranking system and are discouraged by the Search Engines. A so-called SEO expert might sell you on these techniques to make a few quick dollars because as soon as the Search Engines find out that you're using Black Hat Methods - and they will… they have teams of people dedicated to identifying Black Hat methods - you'll get either banned or pushed to page 72 and put on a watch list.
The best thing you can do is EDUCATE YOURSELF, so that you know what you're dealing with when you're talking to someone about doing SEO for your website. Or if you have ALOT of time on your hands, you can do it yourself.
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