Jennifer- You need to have it professionally appraisied (from a certified gemologist) and have a written apprasial from them. You can contact Carnival before you have that to make sure you are in your 30 day window of notifiying them. My wife did this on a tennis bracelet we bought but it appraised at a little more than we paid for it, so we are happy. But she had contacted Carnival because of a ring my mother in law had purchased that was not worth what she paid for it. Did you try CCL's website? I don't know if there is a contact number there for the shopper's guarantee or not. I'll have to find out from the wife how she contacted them.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013