We traveled with Norweigan Cruise Line. And I'm sure my comments will echo comments of all cruise lines. In other words, my issues with NCL are common to the industry.
In a word, the selling of anything and everything to make a buck is never ending. They find a way to monetize most everything. Even when they did something fun like showing you how they made the little animals from rolled up bath towels (which was cute and fun!) they turned around and said a DVD showing how it can be done at home is yours for just $9. It's never ending.
The other thing done, is that the cruise lines are cracking down on guests coming up with excursions through private companies like Avoya or on your own dock-side.
We tried to negotiate a deal with a vender dock-side and was told that NCL had bought up all the spots, and he needed to double check to see if those spots had been filled yet. They hadn't, of course. But it forced us to pay full price instead of trying to negotiate a better deal. That's how NCL (and I'm sure other cruise lines) prevent you from doing that. And they're relentless about having you sign up for excursions with them, rather than with companies like Avoya. For the record, our excursion that we signed up for with Avoya was perfect! Exactly what we hoped for and one of the best of our vacation! Avoya can bring you a better deal on a better excursion than what the cruise lines can offer. That's important to know!