Stone age expansion How trading works question
According to the rules: http://www.zmangames.com/uploads/4/7/1/7/47170931/en-stone-age-ext_rules.pdf 


  A player may:
  
  
  Trade only once his marker has moved off of space 0 of the    merchant track.
  Only trade in order to acquire a Civilization card or Building    tile.
  Trade the resources and jewelry of their choice.
  Improve his trading ability by advancing on the merchant track,    allowing for  2 to 1 ,  1 to 1 , and even  1 to 2  trades. 
  Trade    even if he did not place two figures at the merchant this round. 
  Important: A player may only trade once per round.
  


So you can only make one trade per round