Look at the stone veneers closely. From a distance, most veneers give a stone look, but quality veneers are constructed to mimic the stone upon close inspection as well. Well-constructed veneers have grout lines and imperfections similar to the real thing.
Touch the stone veneer. The texture should feel like natural stone. This requires the right mixture of cement and sand.
Pick up a veneer sample. If the look and feel of the veneer meet your expectations, the next element is the weight. Don't sacrifice look and feel for lightness, but quality veneers that are between 7 to 10 pounds are preferred over heavier ones with the same look and feel. This reduces the stress on the structure during installation and over time.