I purchased a pair of authentic David Yurman lemon citrine earrings last year in St. Thomas at A H Riise. It's on the main shopping street in St. Thomas. As I recall, I couldn't have found them for less on ebay, which is where I buy 90% of my Yurman jewelry. I had just purchased a lemon citrine enhancer, so I got the earrings to match.
I love his jewelry and refuse to pay retail when I can purchase most for 1/2 price or sometimes less on ebay.
Last year on our cruise, I was lured into many shops in the Caribbean looking for a Philip Stein watch. Got back to the ship and checked ebay, and guess what? Some lady needed to unload hers, had the ORIGINAL receipt from Diamonds International in St. Thomas, and hardly wore the watch. Guess who won the auction and saved $150 less than that shop in St. THomas?
Of course, you have to be careful on ebay and only buy from reputable people, which is quite easy to do if you check their feedback.
When we returned to the Caribbean in November, I purchased several Philip Stein interchangeable bands in different colors for a little less than here at Neiman Marcus. Basically, I saved on tax.
I am constantly amazed by the people who are lured in by the hype of the cruise directors. Personally, all we usually buy are t-shirts from the various ports, or win them on board ship in the different contests.
The former posters are correct - know what you want BEFORE you get on the ship and do comparison shopping before you leave for your trip.
Hope this helps.