Identifying high-quality or natural pearls requires specialized gemological testing, which many local shops aren't equipped to do.
Companies like Benadato and Vintage Valuables specialize specifically in pearl authentication and purchase.
Unlike gold or diamonds, pearls are organic and can deteriorate over time, leading to a much lower secondary market value.
Round pearls with a high, mirror-like "luster" (shine) are the most coveted. A Resale Value on Pearls?
Designer pieces from Mikimoto, Tiffany & Co., or Cartier are much easier to resell.