At that time, the futures price was much higher than the spot price, which was unreasonable and there was an opportunity for arbitrage.

You buy the spot at a low price, then register it as a standard warehouse receipt for futures, and then sell these warehouse receipts in the futures market.

For example, the spot price at that time was 3000 tons, and the futures price was 3500 tons. You bought 3000 tons in the spot market, and then sold 3500 tons in the futures market, making a net profit of 500 yuan per ton, without taking any risks, so you dared to mortgage the house and car.