Finding buyers on eBay is more about getting the buyers to find you. eBay does a good job of driving members to the website itself and there's millions of buyers there already looking for something and they already know eBay is for buying so by the time they reach your auction listing their wallets are already half way open.
And this sounds great. All those ready buyers ready to click the 'buy it now' button on your listings.
But there is one problem. Just a small one.
While there's a lot of buyers - there's also a lot of sellers. And the old saying 'build it and they will come' certainly doesn't apply on eBay. Listings for worse products at higher prices will show up before the better ones - if they're properly listed. If you're selling to a popular niche there's going to be more buyers but also more sellers - so your voice becomes muffled out in a crowd.
So there's two ways to answer this.
Enter a smaller niche with less competition and become the big fish in a small pond (or several small ponds if you go after multiple niches) or find ways to help yourself stand out from the crowd in the bigger niches. There's no wrong choice here - both are viable and both have strengths and weaknesses.
Ideally what you really want to do is get yourself into the small pond and use the same techniques as you would in the bigger one to get yourself noticed and make sales. But the important side to this is to not over commit yourself to a niche you know nothing about. So set yourself a limit on how much you invest into stock before you start buying. Buy a couple of items and list them - you can use that money to reinvest into new stock and make sure you make a few sales into a niche before committing further to it.
The more you sell in a niche the easier you'll find it. Each niche will respond differently to different offers so you might need to use a little bit of trial and error to see what works properly in your niche. Remember that eBay has millions of buyers but the people looking for rock climbing equipment are likely to be very different from those looking for rare stamps and therefore will respond differently to different types of offers.
Finding buyers in a niche is as much about making it as easy as possible for buyers to find you - as it is about finding them. People have a much lower attention span online than they'd commonly have in a retail store and you need to make it as easy as possible for them to be able to check your auctions. Sometimes, no matter how good your offer is sometimes certain items just won't sell to a specific niche. On eBay knowing what sells best on eBay is as important as knowing how to find the buyers to sell it to.