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).

We can only infer from the existing connected maintenance records. If the records show continuity and adhere to the recommended maintenance schedule, we will assign a high credit score; if there are gaps of tens of thousands of kilometers, we will assume it was not well maintained during that period and alert you.

The headliner is considered an "irreversible interior component." If the edges are delaminated or there are deep, hard-to-clean dark water stains, it will directly lead to a downgrade in the interior grade, even if it does not affect driving. We will not use pins or low-quality glue for cosmetic repairs.