Experience turbo lag and power surge during road tests; check for significant oil accumulation at the turbo intake and intercooler connections (slight oil vapor is normal); and use OBD to read the real-time boost pressure peak to see if it meets factory settings.

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).

Our legal red line is that the amounts on the China Customs declaration, export license, commercial invoice, and bank receipt must be consistent across all four documents. We firmly refuse to engage in the illegal act of issuing "false low-value invoices" to assist buyers in evading customs duties in the destination country.