First, we need to know that the way of our transaction is Matchmaking Tradeoff. Buyers and sellers will make the deal only when their orders has the same price.
As the picture shows, there are red selling orders and green buying orders On the right side of the trading interface. You could see that the first selling price is ?, the first buying price is , the market price is？
If users want to complete the transaction fast, you have to matchmake with the current best price. Users who make selling orders have to matchmake with the first buying price ? , and buying orders with the first selling price ?. The transaction with market price won't complete until reaching the best price.