First of all if you plan to sell on ebay please know that ebay is a 'BELOW WHOLESALE MARKET'. Most all of the items selling on ebay are being sold way below wholesale prices.
Second, yes, some of these people have huge buying capital and are buying extremely large quantites of goods thereby getting them at a very small price..The larger a quanitiy you buy the cheaper per item price you will get...
Third, if you want make money on ebay you should start looking at purchasing goods in bulk and from liquidation and surplus dealers. Buy doing this you can get items at literly pennies on the dollars and resell them for a nice profit while still selling them at way below wholesale prices.
Check out sites such as liquidation.com and surplus.net. I'm not saying that you have to start out by buying a truckload, but you should probably start with at least a pallet..I see pallets that sell from many liquidators for 2 to 3 hundred dollars and you can turn around and sell that pallet of good for 800 to 1000.
If you can't afford a pallet, then don't be afraid to ask the surplus dealers and liquidators if you can get a smaller lot to start with. Let them know that you are looking to form a long time relationship and you'd be surprised at how many dealers are willing to work with you...