If you send a email to your list promoting a product, how much will be clicked? And how much sells will you get? Questions are little tough to answer. I know many internet marketers who have huge list of subscribers, but they don't get sells as they may deserve. Why this happens?

There are many reasons but most important is your reputation in that particular field. If you are known as a 'Guru' in that field, you are going to get good result. You don't need to bombard your subscriber...