Request a detailed grading report from the supplier. In the secondary market, items are often categorized as Grade A (like new), Grade B (minor scratches), or Grade C (visible wear/dents). Ask for high-resolution photos and videos of the specific batch, focusing on rust spots, weld points, and seat surface condition. For bulk orders, it is highly recommended to hire a third-party inspection service to perform a random sampling based on AQL (Acceptable Quality Level) standards before the balance payment is made.