I agree, it is also good when you are trying to sell a certain amount of goods before allowing them to eat the rest because the price is not high enough anymore.Along with that, they should make that consumables, which are locked in inventory should not be consumed by the army. It brakes "The art of trade" quest, when you are asked to sell the grain or grapes, and your troops simply eat the goods by the time you reach the place where you wanna sell them.
For that quest, i just pay them for the goods, does actually finding a buyer yield more relationship or something?