Dealer, merchant (6)
I believe the answer is:
trader
This clue is a double definition.
'dealer' is the first definition.
(synonyms)
'merchant' is the second definition.
(trader is a kind of merchant)
(Other definitions for trader that I've seen before include "Red tar (anag)" , "Dealer who buys and sells" , "One buys and sells" , "Person in the business of buying and selling" , "One in business" .)