The advantage of an exchange like this is that the seller is free to determine the selling price as he wishes and the buyer can freely look for price variations on the exchange. Buyers can even get a much cheaper price than buying on a regular exchange.
Then there's no difference at all with that description.
As buyers can also simply put up a lower price which how much they want to but the thing is, no one is willing to sell it at a lower price unless the market drops and reaches the price that has been set.