One quick test that normally reveals the fake is to run the pearl gently between your teeth. The cultured pearl will have a mildly abrasive or gritty feel, while the immitation will be slippery smooth. Try the test on pearls you know are cultured, and then try it on known immitations to get a feel of the difference. The cost of being wrong may be too great to risk it. Matching is used to match pairs or match for necklaces.
Pearls are uniform and are as close as possible to each other.
One of the most important factor that will effect the market price of a pearl will be its size. It is important to note that it is the nucleus size, not the growth process that largely determines the end size of the pearl. Keep in mind the factors that affect the quality-size, luster, color, roundness, skin blemishes. Once you know which factors are important to you, and which you can juggle to get the the pearls that are right for you. And so on.