You can sell books and eBooks to virtually anyone. With the release of Amazon's electronic book reader "Kindle", more and more people are likely to be encouraged to buy/download ebooks online from stores such as Amazon.
Amazon can attest to the fact that books and ebooks are profitable anytime of the year. Of course, textbook hard copies are sold in bigger quantities during the opening of schoolyear. Also, the launching of popular children's books such as Harry Potter also help bookstores make more profit.
There are a lot of storefront providers for upstart booksellers online. But if you wish to build your own website you would have to analyze various factors such as how many products you wish to sell, how your site will look like, what type of shopping cart you would have installed, and whether you would have to acquire your own processing software for credit cards or use Paypal or other services as your free internet merchant account (third party credit card processor).
Do you really need a free internet merchant account when selling books and ebooks? Again, this would have to depend on the quantity of the products you are selling. A lot of start up booksellers acquire a free internet merchant account because they do not have to pay for the setup, monthly gateway or minimum transaction fees. On the other hand, if you intend to sell a huge catalog, then it would be wise to acquire a real merchant account that will handle your processing on a good discount rate.