I know I've suggested specialty buildings for villages before but I think I've come up with a nicer way to foster trade.
Just as new building options open up when you attain skills and Lawspeaker I thin there should be special building option only available to villages. I won't recover what i already put forth. I think we should add trade specific buildings to the list. If you can create a village idol specificly for trade and then only choose to build say stores, banks, barter stands, vending stands, an Inn or tavern. Each of the buildings should be able to be locked. This makes it easier to create trade villages and foster trade.
Creating a specialty options can be a great help and ease many trade problems.