expression · to engage in financial speculation, specifically by buying on margin or short selling in the market

他在股市里大肆买空卖空，结果赔得一塌糊涂。

idiom · to deceive or cheat people by selling non-existent goods or posing as a reputable operator

这个中介并没有实际房源，只是在买空卖空，骗取客户的定金。