Unless I've missed it, no place in the expansion rules does the merchant affect the economy. House rule over here is that it does (except when it can't), with no other changes to the merchant, so that there is some resource churn outside of the PC's. Thoughts?
Behaviour Cards for the Solo system.
The Collector buys cargo; Market Manipulator discards cargo from Economy board.
Some of these behaviours could be fun to add to non solo game.