If you are buyer, market price = 賣出價;
if you are seller, market price = 買入價.
For example, the bid/ask price for #5 HSBC is $99/$100, (1) when you are buyer, the market price (to complete the deal) is $100, you will buy it at $100@; (2) when you are seller, the market price (to complete the deal) is $99, you will sell it at $99@.