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 will check if the vehicle identification number (VIN) is within the official recall batch. If there are any outstanding safety recalls (such as replacing Takata airbags), we will require the original owner to assist in sending it to an official 4S shop to complete the free recall work before the vehicle is deregistered.

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.