Let's say Alice is selling 1 BTC for $10,000. Soon after Alice makes her sell order, Bob places a buy order for 1 BTC for $10,010. These two orders are compatible, since Alice would gladly take an extra $10.
My question is, what happens to that $10.
- Does Alice receive $10,010 even though her sell order was only for $10,000?
- Does Bob only have to pay $10,000?
- Maybe they split it down the middle, Bob only has to pay $10,005 and Alice receives the same?
- Does the exchange just keep the difference? Is this how (in addition to the fees) exchanges profit?