There is an unbelievable amount of car rental services competing for a prospective customers business. A person can feel that they have no chose but to give into whatever the customer service representative request, no matter how unpleasant the service they provide. After leaving a flight that is unusually difficult or uncomfortable, the thing that can make it worst would be if, the car that was suppose to be reserved for them will not be available after all. This is why car rental companies ask for flight number. Hopefully by doing this it will avoid future problems.