Existing studies on low-price guarantees (LPGs) typically employ static models and the results are sensitive to modeling assumptions such as the type of guarantees, hassle costs and consumer heterogeneity. In contrast, we employ a fully dynamic model and show that LPGs robustly facilitate tacit collusion, by reducing a deviating firm's immediate deviation profit. This difference of results is because in a static model, any equilibrium has to be immune from any deviation, including infinitesimal deviation. In a dynamic model, however, one can ignore infinitesimal deviations since firms never have an incentive for such deviations.