They will refund your money, if you cancel your tour more than 24 hours before departure. They even refunded our money once on the same day. We had booked a snorkel trip in Curacao. When we awoke, it was storming, not just raining. Lightning, thundering, really high winds and torrential rains. We went down and canceled and fully expected to lose our money. The tour operator called and canceled, so they did refund our money.
We haven't been on Princess for over a year now, (too long I know) but they did not charge my credit card until we boarded the ship. I'm not sure if this has changed since it seems everyone is charging you cards before you board. At least Celebrity and Carnival did on my last 2 cruises. I haven't booked one on the Epic, yet, because I still have to make final payment shortly.