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
If your purchase was recent (within the last 30 days), you can return it for a full refund to the original payment method. Since Tiffany itself won't buy your jewelry back,
: You can trade in your original Tiffany diamond engagement ring for a credit equal to the original purchase price. How to Sell Your Tiffany Jewelry for Cash
Unlike a pawn shop or a precious metals dealer, you cannot walk into a Tiffany boutique with a silver necklace or a gold bracelet and walk out with a check.