Since Tiffany itself won't buy your jewelry back, you’ll need to look at the secondary market. Tiffany jewelry holds its value much better than unbranded pieces due to the brand's global prestige.
: The diamond must be an individually registered white or yellow solitaire (typically .18 carats or larger) and must be in "immaculate" condition without chips or damage. How to Sell Your Tiffany Jewelry for Cash does tiffany and co buy back jewelry
The Reality of the "Tiffany Buy Back": What You Need to Know Since Tiffany itself won't buy your jewelry back,