Selling commonly available used books promptly on a reverse-auction marketplace like Amazon often requires some "visibility" on the listing page. In other words, your chances of getting a prompt sale depend on your being somewhere close to the lowest few listed books. Otherwise, shoppers need to scroll to find you, and most of them won't bother for a run-of-the-mill book.

For scarcer books, of course, it's prudent to price your listing in the higher range. Customers who are shopping in this upper price range pay lots more attention to the condition, shipping options, and of course the seller's feedback and apparent care in writing the description. Here you're competing more on service and reputation, not merely price.

If you've got a scarce book, check to see whether there's a pending order for it on Amazon. Go to the book's product detail page (by searching for the ISBN) and click the "Sell yours here" button. Click through to the next screen and, if there's at least one pending order, you'll see an orange box labeled "BUYER WAITING." You can close your browser before clicking to actually list the book.

For scarcer books, you'll need to do more research. It's not unusual, for example, to see two copies of a book for sale at dramatically different prices - for example, one priced at $10 and the other at $100. Both are used, not collectible. Obviously, one is priced wrong. How do you find the correct value?

For most books that are not exceedingly scarce, a quick check at a price-comparison (or meta search) website will yield a more accurate picture of a book's value. Click here for examples.

These sites will show you the lowest prices on all the major bookselling venues. If you still don't find many copies, it's best to play it safe and price your listing high until you can research further.

Out-of-print books are the bread and butter of the online bookseller. When the supply of a title is finite and demand is steady or increasing, prices naturally rise.