Actually, as far as airlines go, as long as you let them know within 24 hours you'll usually get a full refund no strings attached. Different airlines have slightly different policies. For some, you need to request the refund strictly within 24 hrs. For others, you can get the refund anytime before the next day ends. This is the case for all of the airlines I've had to get a refund with in both Canada and the USA.
Beyond that grace period they'll usually charge a fee of some sort, and the refund might be in the form of a voucher or credit.
Beyond that grace period they'll usually charge a fee of some sort, and the refund might be in the form of a voucher or credit.