Using a sample of insider sales from firms listed on China's A-share market from 2010 to 2023, we provide robust evidence that insiders engage in fast sales when stocks have better pre-sale performance, compared to slow sales. Additionally, these fast sales predict lower abnormal returns in both the short and long term. Insider opportunistic trading through fast sales is more prominent in firms with high levels of information asymmetry and among insiders facing intense information competition. We find weak evidence that independent directors, institutional investors, and analyst coverage play a role in reducing such insider opportunistic trading. Finally, insider opportunistic trading through fast sales also predicts subsequent stock price crashes and extremely negative earnings news. Our findings help decipher the information content of insider sales in China's market.