The Collaborative International Dictionary of English v.0.48:

Marketer \Mar"ket*er\, n.
   One who attends a market to buy or sell; one who carries
   goods to market.
   [1913 Webster]

WordNet (r) 3.0 (2006):

marketer
    n 1: someone who promotes or exchanges goods or services for
         money [syn: seller, marketer, vender, vendor,
         trafficker]