I've heard that people think that trading should be done item-to-item, and that is all good and fine, but then... it is more difficult and complex, to have a list of things that are equal value, without having mix-ups between items that aren't on those lists... (almost confused myself there...)

So, here is my idea (and I know it has already been discussed), being able to have a tribal banking system that allows you to, not only fix a suggested price, in currency, for items, but allow item-to-item trade on a more level field, based on supply/demand within that tribe.

With this as a basis, we could trade over larger distances and create courier quests for those that wish to make extra money, not limited to 'foreign' tribes that don't actually exist in the physical game-world.

References:
http://en.wikipedia.org/wiki/Banking