Among other reasons (black market, back of truck special and the like) these people may be purchasing reselling large volumes of the items, instead of making a $10 profit per item and selling 10 items to make $100 they are trying to make a $2 profit per item but selling 50 items to make $100. This is usually true if the same seller has a large quantity of the same item listed at the same time.The same theory applies to why WalMart can sell stuff cheaper that your local grocery store.
Some people hit clearances and some hit flea market and or yard sales.You just kind of got to know what to look for. Upscale clothing, suits etc are good. My father works for a department store, and a nice one at that, sometimes to clear out the racks for new merchandise they mark things at 75-80% off, which is below their cost.My husband is 6 7 and I have to buy talls so going through my dad I buy my husband $125 shirts for sometimes as low as $9. I could sell them on ebay but I don t. There are people that shop his department and buy out the rack and do just that.
Try this software at http://wholesaleproductsearchtool.com I know that many ebayers use it to find products and it is 100% free.
Black Market.