hi guys,

this is how i do it. first realise that your capitol location changes the value of every resource in the game. also realise that income for a resource also depends on the skill of the merchant.
first i make 2 merchants asap at start of game and put them to work in an region owned by me with 2 of the same resource type. one of each. they will then get monopolist line of traits. when they are level 4-5 i move them to the resource they will make the most money on preferably 3-4 moves turns away then they will get good traveeler traits.
then i leave them there and attack any lower level merchant to come along.
attacker has the advantage unless the defender is on a resource trading. in that case defender has advantage.
i then make new merchant.
i max out merchants as i do priests. once you have access to good resources you merchants will make 100-600 per turn and quickly exceed purchase price.
what you must not do is make new merchants in areas populated by even one high level foreign merchants.
some people use their high level merchants as hunters and get the massive rewards for acquiring high level foreign merchants. for me this involves too much micro-management and i prefer to fire and forget. if i notice an opportunity i will take it but otherwise too much like hard work.
merchant guilds make better starting merchants. also they give trade bonus to the city hosting them. i never reject merchant guild and often wait for one to be offered.