The "price" is whatever the last trade went for. If there are market manipulators buying up "all the shares", it would seem like a big risk as they are relying

The "price" is whatever the last trade went for. If there are market manipulators buying up "all the shares", it would seem like a big risk as they are relying on there being enough bids within their profit range to sell them back at a profit. Right now for example, you could sell 100 BTC on Mt.Gox for an average price of $203USD/BTC. Try to sell 10,000 BTC and the average drops to about $195, and 100,000BTC would only average $111.