How to sell Premium Content?

1.
For the web sites and blogs there is another technique for earning money. Some of them offer free access to some of their contents but charge for their accessing their premium contents.
SEOMoz is one of such site that offers you good example. This is very popular blog and gives information and advices on SEO related matters. In case the visitors like them and they can become a member against fee. They are now called premium members and have access to exclusive materials, tools etc.