Ok, let me break it down this way.
Its called a penny auction, now I have not looked at the cost of the bids but lets just say the bids are .50 cent each.
How this works if you "pay" for bids. You buy a lot for X amount. If each bid costs .50 cents (each bid placed is only for .01) and say a $500 rifle sells for $100 that means that 10000 bids were placed. They made $5100 to sell a $500 for $100.
Take in to mind that these numbers are not "correct" but it will give you a idea of how it works.