WordNet (r) 3.0 (2006):

horse trader
    n 1: a hard bargainer

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "horse trader":
   Artful Dodger, Philadelphia lawyer, Yankee horse trader,
   bunco artist, bunco steerer, cardsharp, cardsharper, carpetbagger,
   charmer, con artist, con man, confidence man, crafty rascal, crimp,
   dodger, fox, glib tongue, horse coper, jackleg, land pirate,
   land shark, land-grabber, mortgage shark, pettifogger, pitchman,
   reynard, shark, sharp, sharper, sharpie, shortchanger, shyster,
   slick citizen, slicker, sly dog, slyboots, spieler, sweet talker,
   swindler, trickster