Another "what's the catch" would be a cruise ship docking in a faraway pier - like in Barcelona or Stockholm - where you can't get anywhere without using a taxi - and they don't tell you.
There is one cruise line (I won't say the name) which commonly would dock at a pier where the only way to get anywhere was to use THEIR shuttle which came at a cost. Other cruise lines would have free shuttles, but not this one.
They would tell the people who asked - but they didn't make it a priority to get the word out.
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.