We use two steps: 1. Insert a medical-grade endoscope through the spark plug hole to visually inspect cylinder wall scratches and carbon buildup on the piston top; 2. Extract an engine oil sample to check for large metal debris or emulsification (caused by coolant leakage).

We use quantitative standards. Minor scratches less than 3 cm that do not reach the base coat (which can be polished) are considered normal wear; scratches over 3 cm deep to the base coat or dents larger than 2 cm in diameter will be highlighted in the inspection report's "Appearance Defect Distribution Map" with close-up photos.

Due to legal restrictions preventing unregistered vehicles from high-speed driving on public roads in China, most of our dynamic tests are conducted in a closed area (with a maximum speed of around 60 km/h). This is sufficient to test for suspension noise and low gear smoothness, but it cannot simulate high-speed wind noise and tire balance vibrations at 120 km/h.