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).

China has a large number of luxury cars and a fast turnover rate. For luxury cars of the same year and mileage, the FOB offshore price in the Chinese market usually still has a 10%-15% arbitrage opportunity after deducting shipping costs, especially for models with high depreciation rates.

4S dealership records are directly connected to the manufacturer's database, making the data hard to tamper with and the most reliable, with original parts guaranteed; third-party repair shops usually are not connected, making their data unverifiable. Therefore, we only consider the connected records from 4S dealerships as valid historical documentation.