I have spent few hours to do a research and it's not as easy as many people think. The biggest problem, what I see is with choosing the right product and secondly with a marketing. The money that generates the eshop is fabulous, but there is a big chance that you spent a lot of money at the start and you will not succeed.
You have this not succeeding risk in every business. Online businesses are more cheaper than the offline business one has. Think about a clothing store which has a show room in your mall.
How much they spend a month for rent, electricity and others?
How much they spend to pay the staffs every month?
How much they spend in marketing?
In e-commerce you do reduce a lot of these costs nearly to zero.