No I think you'll find that stealing things is always far more profitable than trade. You smash your way in, grab what you want and then go back home all in the style of space vikings. Of course each raid becomes more difficult as you have to face prepared defences and possibly some X-COM type force. So the solution is just steal all you need first time around. Of course such action will not win friends and will make an entire planet distrustful of aliens and out for vengance.
But it would be more profitable than trade, as what do we have to trade that has any value beyond raw materials? (Unless we are the ultra violent species of the universe, in which case contract mercenary work bekons.
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