Use the following factors to evaluate any piece of cultured pearl jewelry.

Lustre - The surface should be bright, not dull.

Surface - The fewer blemishes on the surface of a pearl,
the more valuable it will be.

Shape - The rounder the pearl, the more valuable it is.
Cultured pearls also come in oval, pear and baroque shapes.

Color - Cultured pearls come in a wide range of colors from pink to black.

Size - Cultured pearls are measured by their diameter in millimeters.
With all other quality factors being equal, the larger the pearl, the more
valuable it will be.

Matching - When buying a strand of cultured pearls, matching is important.
All the pearls in a good quality strand should be evenly matched in terms
of luster, surface, shape, color and size.