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.

We maintain an absolute skeptical attitude. In addition to regular visual inspections, we focus on checking for sediment accumulation around the sunroof drainage channels and look for water stains under the A-pillar trim and front floor mats. This is the only effective physical evidence to determine if the sunroof drainage holes are blocked, leading to hidden leaks.

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.