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).

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.

Based on practical risk assessment, we strongly recommend setting aside 3% to 5% of the car price as a buffer fund for even the highest-rated used cars, to cover oil changes, new tires, minor shipping scratches, and local inspection labor costs.