Traders have some ability to sell "exotic goods", which if I remember correctly shows up as a function of your trading skill. I don't know if there are any distance modifiers.
When a trader sells food there seems to be a chance you will also sell exotic goods, that you magically purchased without knowing and that you will sell without the game asking if you want to. The chance seems to be based on the distance between the purchase point and the sales point and trade skill. At least I never saw this while selling inside a realm but I did a few times from transporting food from one realm to another.
