Southern Hǎinán is famous for its cultured pearls and infamous for the persistent saleswomen who flog them on Dàdōnghāi beach, though in fairness they're not that bad. Most of the pearls are genuine, if not good enough to make the export market, and sell for just a few dollars. But there are some cases of people being duped into paying for fine-looking plastic. If in doubt, scratch away at the pearl - if it's plastic, it should flake or chip; a real pearl won't.