That is a terrible economy structure. Basically "The Guy in the castle pinky swears not to screw you over" ugh...fucking disgusting.
Granted, Roland is a feudal Lord. These are his lands and the 'reward' is being allowed to govern pieces of it and make earnings directly from him if he deems you've done a good job running them. That may be capitalistic in nature, but business begins and ends with the governing body.
Also, for everyone saying this is communism-close, but not quite. Communism would eliminate any and all forms of profits (excluding favors because the ruling class wants you around). This is more akin to fascist economics where you can run a business, it'll be recognized as your business, you'll be compensated with earning for working, but the government can and will tell you to kiss the ring. I might shooting a bit to far-this is a feudal system like I mentioned before-but that's the gist I get here.
Edit: Gave it some thought and I believe they aren't allowed to sale the grain in the open market because they're Serfs. It's not exactly communistic and is actually a bit more capitalistic than I thought.