We sailed on Carnival and had a guarantee inside cabin - this was a last minute cruise. There was a problem with the plumbing bubbling up through the shower drain. The smell was terrible. We asked for a new cabin which we got one (another inside cabin). The following evening a bottle of red wine was brought to our dinner table, compliments of Carnival. It was on the menu for $70. We also got a letter appologizing for the inconvenience and a coupon for 10% off a future cruise.
We were happy with our new cabin change - and the rest was all unexpected but appriciated.