There are many heavy hitters out in the eBay marketplace. Many list hundreds of items and work on the saturation means of getting sales. Some only make about $1 an item but ship over a hundred per day.
Some literally spend 12 to 14 hours a day doing eBay and have several computers going with many accounts.(I won't get into that.) Some of the more experienced sellers work out the search metrics and how to get their items up in front of the most people.
One trick was to overcome the MS software limit by spelling Microsoft Micro Soft which worked until recently. Don't try it you'll get suspended.
Some find their listings not showing and or showing far down the pages and figure out how to get them up top.
My take on this is if you want to make it big on eBay, you have to want to spend your whole day on the computer constantly looking for suppliers and niche products.
Example: I saw one guy selling route 66 signs. Real highway signs. And his story was that he picked them up from a town along the route found in a back room. I know where to get them and have an account with that company. He was selling them by the dozen for about a month and making about $50 profit per sign until others caught on and saturated the market.
He probably made 2 to 3 g's on that niche until it dried up.
I'll bet during the time he was selling the product he was working on his next niche product every waking hour.