If you sell used books on Amazon.com, you can save a significant amount of listing fees by becoming a "Pro-Merchant" seller.
The choice of whether to go Pro-Merchant is a no-brainer after you've been selling a short while. Once you're selling an average of 1.4 books per day, the subscription pays for itself since Amazon waives the 99-cent closing fee nonsubscribers pay on each Marketplace sale. And obviously, as your sales increase, the savings multiply because all those 99-cent fees are history.
Unlike eBay's Powerseller program, Amazon Pro-Merchant status does nothing to impress buyers. But it provides a crucial tool for managing your business: the Inventory Loader. This enables you to upload and download your book listings using a text file or third-party software. You'll need the Inventory Loader after you have more than a few hundred books for sale -- if you want to keep your inventory organized and priced correctly without having to hunt and peck through Amazon's Web pages.
Back when I started selling, switching to Pro-Merchant was a hassle because you had to manually close all your listings and relist after your subscription started. Fortunately, that's no longer necessary.
Since you're just starting, there's no need to decide immediately. You can test the waters, and if you enjoy selling and want to expand, the advantage of going Pro-Merchant will be increasingly apparent.
If you go Pro-Merchant and later decide it was a mistake, you can always cancel the subscription. At that point you'll have the option of keeping your listings open and continuing to sell as a non-subscriber. Or, if you've had enough of bookselling, you can close your listings when you stop your Pro-Merchant subscription.