When sourcing medicinal mushroom products like Reishi, Lion's Mane, or Cordyceps, the most critical factor is the active compound content, specifically Beta-glucans. You should demand a Certificate of Analysis (COA) that specifies the percentage of Beta-glucans rather than just 'total polysaccharides,' as the latter can be inflated by adding starch. Additionally, ensure the supplier uses dual-extraction methods (water and alcohol) to guarantee the bioavailability of both water-soluble and non-water-soluble compounds.