I actualy found the answer in a nearby thread titled "recorses"

"you can also change the value of the trade goods

in the same file startpos/early.txt or whichever era

DeclareTradegoods:: "GLASSWARE" 40
DeclareTradegoods:: "WOOD" 20
DeclareTradegoods:: "FURS" 40

the number indicates the value of that good in trade just fiddle up or down for preference. at the bottom if the list is also the import percentage. this is quite insignificant, but sets the percentage of the above figures to be used as the import rating for that good, when the AI trades with you. its currently set to 10/20% but raising it makes AI trade more worthwhile but will also give the AI factions more money from you tradingwith them in theory, this is also the place where you can add in new tradable goods simply by declaring them, but its more complicated than that, of course... "