I never leave home without my jewelers loupe.
when I was a cruise with Carnival the sales clerk was so nasty told me I had nerve asking her for one. So I whipped mine out and checked the gems.Got similar one,cheaper in Cozumel. I never go to the "authorized stores" Sound like "kick back" to me.
I'm not saying you can't get a good deal on a gemstone, but buyer beware. Also the settings are not always as secure as your local jeweler.My dad bought me a nice diamond/ blue topaz ring from Aruba, well I wore it to dinner stone popped out.(I found the stone but still) My jeweler told me they did shotty work on my setting, and he re did it. I know my dad paid a lot for it.
Then again I know friends who buy jewelry on their cruises and had no issues.