Whether you know what you want to sell or you have no idea, you should start by checking out what people are buying at eBay. There are several ways to find out.
eBay Marketplace Research. You can get the most thorough eBay purchasing research by subscribing to the eBay Marketplace Research service. (You can find it on the left navigation bar on the eBay homepage.) This service compiles the previous 90 days of eBay auction sales data and provides detailed reports that can be viewed in various time increments. There are three levels of fees for the service: fast pass for two days ($2.99), monthly basic ($9.99), or monthly pro ($24.99). Try the fast pass and search by item type or name and then filter the results to find information such as the number of bids, completed sales, and average sale price.
As an example, we researched opening an audio book business. We learned (see chart below) that the average sale price for an audio book during the past two months was $11.32 and that approximately 25,000 audio books were sold. Further research indicated that one of the better-selling subcategories in audio books was children's audio books, particularly classic fairy tales. So, if we were to open an eBay audio book business, it would be wise to pay less than $7 or $8 per unit for audio book inventory, and it would be wise to stock children's classics such as Cinderella and Little Red Riding Hood.
Example: eBay Marketplace Research Results