When sourcing an original or custom-designed product, you must prioritize Technical Specification Documents (TSD). Ensure the supplier can interpret CAD/3D drawings accurately and provides a Golden Sample for approval before mass production. Key performance indicators should include material composition analysis, structural integrity testing, and adherence to industry-specific certifications (such as CE, RoHS, or ASTM). For original designs, verify the supplier's R&D capability and their ability to maintain tolerances within ±0.05mm if precision is required.