Classes of Service. Airlines also offer special excursion fares which are cheaper than normal, but which come with restrictions as to how long you must stay at a certain place before flying back or how far in advance you must book the flight. If you cancel such a flight, you'll probably lose a percentage of your money. On the other hand, if you just show up at the airport without making a reservation, and there happens to be room for you on the airplane, you'll end up paying much more than excursion fare, sometimes twice as much. Airline travel, more than any other kind, works out best if you plan it carefully in advance.
Shuttle service exists between some major cities, like New York, Boston and Washington.
You do not need reservations for shuttle service, you just show up and board the plane. The fare structure is complicated. It is here that a travel agent can help you. You will never pay more with a travel agent than you would by dealing with the airlines directly, and a good travel agent can save you money. Nearly all airlines accept major credit cards, and travel agents accept them for airline bookings also.