I can't blame this on DI because I don't remember the store.
I had tried on a ring that I fell in love with but it was too small. It was a channel setting with diamonds all around the band like an eternity band. I suspected it would be very hard to size a ring like this - basically softening/stretch the gold to make it a bit bigger because it would weaken the channels or create a spot where there was no diamond. I'm sure it can be done, but its not a job to be rushed with a customer waiting to make it back to the ship.
The store insisted on try to make it fit on my finger, but it wasn't going on (nor did I want to be stuck buying it because they forced it on). Then they offered to size while I waited but I declined. THey really did not want me walking out of that store.
Came home and hired a jeweller here to make me the ring. Cost me only slightly more than what I was getting it for in the islands, and I felt much safer with a ring made for me and an appraisal I could trust.
I think anytime you buy in ports you're taking a risk. Sure the cruiseline "endorsement" helps but it doesn't sound like they were too helpful in this case.