If you want a short lesson in online selling, look no further than Amazon.com.
Pull up a book or product and take a look at what they´re doing.
There´s a professional photo or graphic of the product. The price is there, but it´s combined with an offer (usually free shipping), and it shows you how much you save off of retail. This latter point is important and probably worth another post. Telling people what something is worth and that it´s currently selling for less than that is a compelling, proven advertising strategy.
Amazon listings also tell you how many of the items are in stock and how soon you can expect to receive one. When shoppers know that quantities are limited they´re more inclined to purchase, of course. Setting shipping expectations is good practice for everyone involved. They cross-sell, showing the shopper another product that goes well with the one being considered. And they have this section with links to other products that people considered when they were looking at this one — another cross-selling tactic. For some of the books you can "look inside the book," which is kind of like letting the customer pick up the item and examine it more closely.
There are customer reviews — which act like positive testimonials in most cases. The main "editorial review´ section describes the product in detail.
Further down the page, Amazon includes all kinds of cross-selling and interactive devices, like customer discussions (which generate interest around specific topics and products), Wiki information that describes products further in a open source fashion, Listmania (customer "top-ten´ lists of books or products like the one you´re considering), and much more.
Do just a few of the things Amazon does, and you´ll increase sales with your auctions or eBay store. Think testimonials/feedback, offers, description clarity (in both photo and body copy), setting expectations, limited quantities, extensive access to information and interactive involvement (Wikis, discussions, etc.).