When sourcing embroidery patches, the stitch density is the most critical factor; high-quality patches should have no visible backing fabric through the thread. You should verify the border type, choosing between merrowed borders for standard shapes or heat-cut/laser-cut borders for complex, custom geometries. Additionally, ensure the supplier uses colorfast polyester or rayon threads that won't bleed during washing, and check that the backing material (iron-on, Velcro, or adhesive) is applied evenly to prevent peeling.