All online bookstore owners need POS software to run their business. In my previous posts I mentioned some open source e-commerce shopping cart that they can use to start and manage their online bookstore. Because the open source software are free, store owners only need to pay the webhosting package and install one of them for their online bookstore website.
I recommend OS Commerce and Zencart for your online business. However, if you are interested in a licensed software for security reason, you can buy VPASP. I do not want to give any comments whether licensed software is better or not because the security of transactions in online stores greatly depends on a lot of factors. Zencart or OS Commerce use mysql database system and PHP language to power the online store whereas VPASP uses ASP programming language. When dealing with customers, online bookstore that is powered by the software deals with the customers directly meaning that store owners or cashiers do not have to input each transaction data into the POS (Point of Sales) software of the store computer. All the transactions run automatically. Store owners will processed the transaction from the back office web-page of their websites.
I personally have tested both Zencart and VPASP. I prefer Zencart to VPASP because it is free and scalable. With Zencart e-commerce software, we can sell not only books from our online retail store but also music and e-books. I suggest that you install zencart or vpasp in your computer and practice using it before you can really start your own online bookstore. If you don't practice using it offline, you will not be familiar with its features or functions and as result your bookstore may not run properly when you operate it online.