Very valuable and rare antiques sell very well on Ebay. Below-wholesale-cost new electronics also sell very well on Ebay. There are lots and lots of things that sell well on Ebay.
For most of us, though, the question REALLY is "What sells well on Ebay that I can find at a reasonable price and sell at a reasonable profit?" Answering that question takes a lot of time and research. You can start by figuring out what type of merchandise you are interested in--since you will be spending a lot of time finding and selling merchandise, and will need to educate yourself about the merchandise, it will help tremendously if you sell something you are interested in.
Next, look up merchandise in your area of interest on Ebay and see what sells and what doesn't. Then, find out how you can obtain the merchandise you want to sell. For some people, this will mean finding a wholesaler; for other people, this will mean going to auctions, estate sales, yard sales, etc. And others will find they can hand craft the merchandise they sell on Ebay. I even know soimebody who buys stuff on sale at retail stores and tries to sell the items at a profit on Ebay.
Although I'm sure there are some rare people who have found an easy way to make a living on Ebay, for most people it takes a lot of work and a lot of time. It's so much fun, though, isn't it? For me, I'm not making a full-time living, but I have a real profit-making business and I really enjoy it.
