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 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.

If insurance claims records are accessed, there will usually be notes like "the insured vehicle is fully responsible for hitting a fixed object" or "third-party liability insurance payment." We can roughly reconstruct the accident scene based on this and cross-verify the stress points on the vehicle's frame with paint thickness gauge data.