Tradegoods are mostly useless.  Therefore, finding a market where a rare
good is sold provides no immediate benefit.  Only when you haul the item
to a consumer city do you collect the gold.
Now you can tell someone else about finding the item, or you can haul it
there yourself, but either way, I don't think the spirit of trade has been
violated.
Regarding the Gatecraft/trade dilema:  I'm going to make a gate-aware
distance routine.  End of problem.  :-)
-- Rich Skrenta <skrenta@rt.com>