ABSTRACT We study how insider trading based on private cost information affects product market outcomes when firms differ in cost variance. In our model, managers exploit firm‐specific cost information to pursue short‐term trading gains, leading them to adjust output decisions and reshape product market competition. We show that trading opportunities have heterogeneous effects on firms' production and value: firms with high cost variance overproduce, whereas those with low cost variance underproduce; correspondingly, the value of firms with high cost variance rises, while that of firms with low cost variance declines. These results demonstrate how heterogeneous costs and private cost information create real economic consequences by linking insider trading incentives to distortions in product market competition and firm value.

Short sellers actively exploit trading opportunities from insider sales. We argue that, in response to concern about potential order flow information leakage, insiders strategically disguise their order flows to escape trading competition. Our model predicts that, when short sellers are sensitive to order flow information, insiders are more likely to adopt a cautious trading strategy, i.e., splitting their trades over time. Empirically, we identify cautious trading by tracking consecutive transactions at the insider-strategy level. We find that, when anticipating intensive short selling potential, (1) insiders tend to trade cautiously; and (2) cautious insiders tend to reduce their initial trades. Overall, we highlight the strategic interaction between insiders and short sellers on the diffusion of order flow information.