When sourcing green tea seeds, the germination rate is the most critical metric; high-quality seeds should have a viability rate of at least 75-85%. Buyers should request freshness certificates, as tea seeds are recalcitrant and lose viability quickly if not stored correctly. Ensure the seeds are plump, heavy, and dark brown in color. A common field test is the 'sink test': place seeds in water; those that sink are generally viable, while floaters are likely hollow or dried out. Additionally, verify the moisture content, which should be maintained around 20-30% during transport to prevent embryo death.