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.

We thoroughly rule them out by checking if the cabin wiring harness is melted, if the seat belts have water stains or mold, if there is unusual rust or debris in the seat tracks and cigarette lighter, and by verifying with the insurance company for any "total loss claims." These two types of cars are an absolute sales ban for us.