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Suppose you are running any business and you want to sell product to paid custommer then you have to make your blog private. By doing this you can only allow to paid custommers.
By default, your blog is completely public, and can be read by anyone on the internet. However, if you want to keep it private, just click on “Edit” under the Blog Readers section in the Settings tab.
Under the Blog Readers heading, you’ll probably see “Anybody” selected as the default. When you change this to “Only these readers,” you’ll get an option to add readers.