Through contract trading, it can be allowed to sell first, and then buy and close the position when the price falls. Also make a difference.

For example, suppose the current soybean price is 10, and you predict that the price will fall after a period of time. At this time, you can borrow a batch of goods and sell them at the price of 10. When the price drops to 9, you can buy the same amount of goods at 9, and then return them. After returning, the price difference you earn is 1.