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).

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.

If the car has been maintained at an authorized dealer, we can extract the desensitized official maintenance history (including entry time, mileage, and maintenance items) through a paid third-party data provider and provide it to you. If some year records are missing, we will honestly inform you that the "records are incomplete."