Pilots on charter flights do not ask for the weight of each passenger' rather, they use a predetermined average weight per adult and per child. Also, the maximum weight limitation on an airplane is mostly an issue for take-off performance, not for cruise. There is no way a pilot would take off if the plane is overweight. A lot of fuel is burned during takeoff and climb. The plane cannot be overweight in cruise, since the plane is getting lighter by the minute due to burned fuel.