Then go into your research tool (Terapeak, Hammertap, completed listings, whatever one you use) and research what the accessories sell for. Next, you would go online and try to find a supplier for the product, and determine if you can buy the item at a low enough price to resell it for profit. A supplier could be a wholesaler, a closeout center, outlet store, membership club like Sam's or Costco, etc. This is the hard part - finding the product at a low enough price to resell for a profit.
Keep in mind that niche products will change over time, sometimes only a few months. For example, a few years ago, a VHS tape rewinder or cleaner might have been a hot niche product. But now, it would not be. Same holds true for analog cell phone accessories - nobody needs those now.
Try using this technique and see what you can uncover!
Click here for a list of 395 eBay friendly wholesalers along with 5 important facts for choosing profitable wholesale products to sell on eBay.