The Collaborative International Dictionary of English v.0.48:

Booking clerk \Book"ing clerk`\
   A clerk who registers passengers, baggage, etc., for
   conveyance, as by railway or steamship, or who sells passage
   tickets at a booking office.
   [1913 Webster]

WordNet (r) 3.0 (2006):

booking clerk
    n 1: someone who sells tickets (e.g., theater seats or travel
         accommodations) [syn: ticket agent, booking clerk]