You need to be fully aware of the commitment you are making. A lot of work will go into the preparation and research of your charter both prior to contract and far more once you have committed. Different cruise lines have different contracts, but all will be expecting you to pay for the charter irregardless of what may happen prior to the sailing date. The cruise line, upon signature of the contract, will pull your cruise segment from its selling inventory. If you are customizing the itinerary, the line is building other cruise segments around your embarkation and disembarkation ports. So the penalties for cancellation are high, up to the full amount of the charter. Many cruise lines will do "due diligence" to see if you really are able to meet the commitment. Often they will require an irrevocable letter of credit for the whole of the charter fee.
With yacht charters it is important to be aware of the different contracts used. Some, such as the MYBA (Mediterranean Yacht Brokers Association) stipulate that ALL expenses related to your charter in the way of consumables (food, beverages, fuel, water berthing, all taxes, fees etc. which can amount to 25% or more of the charter fee) are additional to the charter fee, plus you will be expected to leave the crew a gratuity, which is today's age means something in the region of 15% of the charter fee depending on your satisfaction with the cruise. Beware of charter contracts that are loosely worded as you might end up having to pay for far more than you originally anticipated.