This past April, I had booked a C1 guarantee on the Crystal Serenity for the Nov. 12, 2019 crossing from Lisbon to Ft. Lauderdale. I would have preferred the cheaper C3, but it wasn't available. The total price for a single was $4915. I always periodically check the Crystal site and upon doing it in June, noticed that the C3 was available. My agent called Crystal and I was able to get the C3 guarantee for $4270. Then, today, while checking again, I noticed that there was no single supplement. I contacted my agent and she got me the C3 guarantee without the single supplement for a total of $3120. So, that's a saving of $1795, just for checking.