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.

Many car owners do not have their first maintenance done at authorized dealerships, leading to gaps in early data. In such cases, we do not blindly trust the odometer; instead, we analyze the tire production dates and wear levels, as well as the depth of grooves on the brake disc edges, using the "gold standard" of physical wear to infer the intensity of early use.

Odometer tampering is a common risk in the global used car industry. We verify the data by extracting transmission mileage from the OBD computer, checking the most recent maintenance record's mileage, and consulting the national traffic management app for annual inspection records. If there are irreconcilable discrepancies or conflicts in the data, we classify it as a tampered vehicle and refuse to export it.