Solid-state thermoelectric cooling is a promising solution for localized thermal management. Accurate evaluation of the cooling performance is essential for optimization and design of high-performance thermoelectric coolers. However, conventional methods fail to capture performance under actual operating conditions. This article examines the measurement uncertainties in key performance metrics, e.g., cooling temperature difference, cooling power, and coefficient of performance, in the context of the heat-flow method. The results highlight that reliable measurements depend critically on both the quality of the thermal interface and the establishment of steady-state conditions. Moreover, the thermal inhomogeneity and radiative heat exchange issues have also been emphasized, and strategies to mitigate them have been discussed. In addition, a practical reference of the coefficient of performance equal to 0.5 at maximum cooling power has been proposed.