I think the more "real-world" factors Caspian can work into the code, the better. Sometimes there are trade imbalances for a number of reasons: weather, for example.

Foodstuffs should spoil, grains should rot if left exposed to hostile weather. Pestilences such as the CoE equivalent of boll weevils. Fresh foodstuffs need to be consumed, salted, or canned. Armor and weapons rust and would need polishing out - that cuts into the profit margin because of time/ whetstones / polishing cloths, etc. Animals age ... just cause that horse is fast now ... well, he won't be so spry 20 years later ... younger animals generally have better meat at slaughter time. Gems all together in a bag should chip and crack because of slamming into each other ... anyway, I think I could keep going on here, but that's enough for now. :)