Do you want natural, cultured, or imitation pearls. Please note that imitation pearls are custom jewelry and they don’t have much value. Natural pearls are next to impossible to find in stores they are also of a lesser value than cultured pearls.
There are choices of the shape of the pearls that you want. Pearls can be symmetrical, baroque, or irregular. Sphere like pearls are most costly and they are greatly sought after. Symmetrical pearls and tear drop shaped pearls should be even all over.
The size of the pearl is a great issue involving the price. The size of the pearl will affect the price. Bigger is better and they are also more expensive. If money is not a big issue size will only matter by your choice.
Depending on how much you want to spend, what kind of necklace do you want? Do you want a multiple strand with smaller pearls which are less expensive or do you want a single strand of larger pearls which are more expensive.
When inspecting pearls under direct light and on a flat white surface. Check every pearl for luster. Lustrous pearls have shiny surface. There should be good contrast between light and dark, as well as strong and crisp reflections. Avoid pearls that have white and cloudy look to them.
What is the pearls ‘orient’ - a play of iridescent rainbow with high quality colors. Ask whether the color is natural or dyed. The latter is less expensive. More exotic natural colors are more effective.
What is the pearls overtones - a tint secondary to the main body color. Pink tones can increase the price and blues can reduce the price. You can verify that the pearls are clean by making sure there are minimal defects such as nicks, cracks, pits, or discoloration.
Turn the pearl around and check it at all angles. The color, the shape, smoothness, and luster cannot all cannot be different on a single pearl.
Roll a strand of pearls on flat surface to test them for roundness. If they are round they will roll more smoothly and evenly. If they are not round you will feel it when the pearls are rolled, it could feel like going over a bump.
There are three steps you need to take to recognize real pearls from imitations. Run the pearls along the bottom edge of your teeth. A real pearl will feel gritty and or sandy. A fake pearl will feel smooth.
Look at and feel the pearls. Flawless pearls and those that feel light when you bounce them in your hands are probably fake. Check out the pearl under a number 10 magnifier ( a loupe). Imitation pearls appear grainy.
This is definitely a process and it is up to you to do whatever you can to check the value of the pearls. If necessary bring someone who is knowledgeable with you.