Quality in cosmetics is determined by stability and ingredient purity. You should request Stability Test Reports (showing the product remains effective under various temperatures/humidity) and Microbiological Testing to ensure no contamination. For color cosmetics, ask for heavy metal testing (Lead, Arsenic, Mercury) to ensure levels are within international safety limits. It is highly recommended to order pre-production samples to test skin feel, scent, and oxidation levels over a 14-day period.