It's terribly frustrating as unless the seller has a receipt to prove it, you just don't know. I try to have them photograph the stone on a dime to get a gauge of things and because I've had several sizes I feel more confident that way. Sadly, I've had friends buy ".25's" on eBay that ended up being only .08 when they arrived. They returned them as SNAD (Significantly Not As Described), after verifying the size being wrong at Tiffany. It's a gamble but sometimes you get lucky and get a bigger one that you thought you'd get. Even if you find one with a receipt, get to Tiffany's to verify everything is ok.
I don't have a .33 to photograph for you. Maybe someone else here does. HTH!
Thank you, everyone! Yes, trying to find a DBTY necklace on the second-hand has been extremely difficult. I've been asking sellers to measure the diamond diameter for me to get an idea of the size.
How do you verify carat size at Tiffany's? Can I straight up ask them or do I compare several necklaces and figure it out myself? I feel like they might frown upon second-hand purchases. Will they authenticate for you at the store? Or is there an online service like authenticate4u that will authenticate Tiffany and Cartier jewelry?