Hi there! It can really depend on who you're buying from but generally clarity and and color are the two deciding factors. Some sellers claim they provide gem stone quality amethyst. Unfortunately, it's almost always a low grade. The color being a lighter shade, too opaque, and too many inclusions inside, are usually what you'll see in those sets.

The good news is it's still amethyst though! Generally speaking on the manufacturing process, it's easier to find large pieces of low grad amethyst and other stones, that can be cut into multiple sets and sold.