The Collaborative International Dictionary of English v.0.48:

Counterman \Coun"ter*man\ (koun"t[~e]r*man), n.; pl.
   Countermen (-men).
   A man who attends at the counter of a shop to sell goods.
   [Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

counterman
    n 1: someone who attends a counter (as in a diner) [syn:
         counterperson, counterwoman, counterman]