If you are reworking Trade I think you should allow lords to sell at a higher price then the max 50 gold. I don't really like the fact that their is a cap on what you can charge for food. I believe price can be determined by supply and demand so if supply is very low because of a drought lets say then I think if a Lord has extra food to sell then they should be able to charge a huge amount for it. If I want to charge a 100 gold for a 100 units of food then I don't see anything wrong with this. I know I personally would be willing to sell more of my food if I was able to just type in what I wish to sell it for instead of having a cap on what I can sell it for.
If the price is to high then people just wont buy.