When sourcing wholesale glass vases, prioritize High-Flint Glass or Borosilicate Glass for superior clarity and thermal resistance. Inspect for the absence of bubbles, scratches, or 'mold lines' which indicate lower production standards. For square designs, ensure the corners are reinforced and the base is weighted (thickened) to prevent tipping, especially for top-heavy floral arrangements. If the vases are for high-end retail, verify if they are hand-blown (unique character) or machine-pressed (uniformity and cost-efficiency).