Buyers must verify the source material, as humic acid derived from Leonardite is generally superior in bio-activity compared to those from lignite or coal. Key benchmarks include moisture content (<15%), organic matter percentage (>80%), and heavy metal limits (Arsenic, Lead, Cadmium) to ensure compliance with international environmental standards like REACH (EU) or AAPFCO (USA). Always request a Certificate of Analysis (COA) and a Third-Party Inspection Report (SGS or Pony) to validate these parameters before bulk shipment.