When sourcing shoulder bags, material selection is the primary determinant of price and longevity. For Genuine Leather, verify if it is Full-Grain or Top-Grain, as these offer the highest durability and 'patina' over time. For Synthetic Leather (PU/PVC), ensure it has a minimum thickness of 1.0mm and high hydrolysis resistance to prevent peeling. For fabric bags (Canvas/Nylon), check the Denier count (e.g., 600D or 900D); higher counts indicate better tear resistance. Always request colorfastness test reports (ISO 105-X12) to ensure the dye does not transfer to the user's clothing.