Some like RCI charge you when you book, others like P&O put them on your on board account and you pay at the end of your cuise. If cancelled you should get your money back. I believe Princess will be same as P&O but not certain.
Hi can only answer for celbrity and RCI, but i would imaigne they are all the same.
if you book online you pay for your excursions at the time of booking by credit card.
if you book on ship gets charged against your sea pass.
if an excursion is cancelled they credit you sea pass with the sum .
Princess and Cunard - you pay at the end of the cruise
they add it to your account.
Princess charge excursions to your on board account (payable at the end of the cruise) whether you book prior to the cruise or when you are on board. We have never had an excursion cancelled, but would assume you would not be charged. Regards, Jean Whittle.
Tip - go to Purser on 1st or second day and get them to input into their system that you wish to pay your onboard accountin Dollars by card at the end of cruise . Dont let them convert your bill " for your convenience " into £ - the exchange rate is terrible. Better still use a fee free credit or debit card.