Hi Julie! This is the first I have heard of this! I am checking into it now, but Tahia has stores on Moorea and Papeete. They offer complimentary shuttles to her store from the pier in Moorea, so plenty of opportunity to purchase there as well. I have a set of pearls from Tahiti, and the quality is great. They are on the pricey side . . . and you are mainly paying for the design and quality of pearls. There are other places to find good quality pearls on Taha'a and Papeete and Moorea as well. Bora Bora tends to be more expensive. And, if the ship has contracted with another Pearl distributer, I am sure the quality will be as good as well.
The other option you might consider is buying loose pearls and having them set as earrings or a necklace when you got home. I did this with two loose pearls about 7 years ago. There was a small flaw on one side of each one, but I had the flaw set on the earring post, so it was hidden and didn't matter. Beautiful quality at 1/2 the price :-) We will have a talk on board to discuss how to pick pearls and the different quality ratings.