When sourcing from traders, prioritize food-grade certification and chemical analysis reports. High-quality salt should have a sodium chloride (NaCl) content of 96% to 99%, with the remaining percentage consisting of essential minerals like iron, magnesium, and potassium which give it the pink hue. Ensure the supplier provides a Certificate of Analysis (COA) for every batch to verify the absence of heavy metals like lead or mercury, and check for ISO 22000 or HACCP certifications to ensure food safety management standards are met.