If the payment is rejected, inform the user. If driver doesn't meet requirements, inform the user. There is a reservation with a given confirmation number. There is a vehicle with a given license number. An instance of rental is created.
Reservation is linked to rental.
Rental is linked to vehicle. The system records a timestamp of when the vehicle is returned. The system creates a return with the date and time in. There is a rental with a given confirmation number. An instance of return is created.