It is a very contrary feature.
Maybe it would be better if the UI showed the price per unit for each thing on both sides. Then it would be obvious that the AI is currently overvaluing their gildar.
I would like to see the price per item vary continuously, rather than being set at the start of a trade.
For example, if I have horses and they have no horses, they might want to buy horses at 10 per horse. They will accept any number of horses at that price, but if you sell them half of your horses at that price, you cannot then sell the other half at that price.
They should instead offer , for example, 10 per horse for the first 10, 9 per horse for the next 10, 8 per horse for the next 10, etc. Until they are not offering much per horse when you are offering enough horses.