How to detect fake pearls
Both natural and cultured pearls are "real" pearls. Natural pearls are incredibly difficult to find and have irregular shapes. Mikimoto invented pearl culturing, in which the oyster is artificially inseminated, after a period of waiting and selection of the best, pearls are brought to market. But both types of pearls, natural and cultured, are totally real.
Fake pearls are those made of plastic, faux, majorica or others. They are artificially created through an industrial process and there is no oyster involved.
To detect these fake pearls the first thing to check is the weight, the fake pearls are much lighter than the real ones.
Other differences are color and birthmarks. The real pearls present changes in the color, while in the false pearls the color is totally uniform. Real pearls also have birthmarks or fishbites.
In a fake pearl necklace the size will be uniform, while in real pearls it varies. For that reason it is usually written between brackets the two sizes of the necklace. (9-11mm)
The classic method to detect false pearls, rub them against your tooth. In the real pearls you will notice a high degree of friction, while in the false ones you will have a soft sensation with the plastic.
Another advice we can give is NEVER buy pearls in Ebay. In Ebay there are thousands of scammers that sell pearls very similar to the real ones but they are fake. They also lie in the titles or dye cheap Chinese pearls black to pass them off as Tahitian pearls.
Both in traditional Jewelry stores and in Internet there are reputable sellers with many years of experience and multitude of experts who endorse the Jewelry pieces.