When sourcing from a factory, you must prioritize outsole material composition, typically requiring high-abrasion rubber or multi-density EVA for shock absorption. Ensure the factory uses hydrophobic webbing (nylon or polyester) that resists water retention. For performance sandals, verify the tensile strength of straps and the use of zinc-alloy or reinforced plastic buckles to prevent breakage under tension. Additionally, check if they offer anatomical arch support and anti-microbial footbed treatments to enhance user comfort and hygiene.