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).

Test-drive cars experience much more mechanical wear due to extreme conditions like cold starts and emergency braking compared to regular family cars. We can identify this by tracing whether the first owner was a 4S dealership or the manufacturer. If so, we will reassess its value based on "operational intensity" standards.

To prevent intermittent failures due to aging of the resistance wire, we will start the engine and set the seat heating/ventilation to maximum for at least 5 minutes, confirming significant temperature changes or airflow output in the cushion and backrest using an infrared thermometer or body sensor.