I've always suggested the game just let the markets go as they will with no star ratings at all and no limits on the trades. Market forces, especially in sentient goods, will correct any problems, and the more acute the problems the shorter the time it will take for the market adjustment. Here's how it actually works in a completely free system. Every resource has a supply (what's available or will be available at a certain time), and a demand (what's needed or will be needed at a certain time). If a player attempts to amass a large amount of a resource the supply shrinks because that player stores the amount purchased in anticipation of selling it for more than he or she purchased it. This drives up the price. When this happens suppliers of that resource may also stop supplying as they perceive the selling price going up, in anticipation of even greater profits. And others will begin production for the same reason. All of which is to say that people are motivated by profit.
At some point though, the scarcity of the product becomes so acute somebody -- usually everybody at once -- begins to sell and the market is flooded making prices plunge. This is a "market correction." What causes that to occur is a complex question and when the prices will start to "tumble" is related to "market timing."
Market timing is the system of anticipating when the market will reach it's "high" point (or low in some systems), and selling before everybody else. It's like a game of chicken with a lot of participants. (It's also a really, really risky investment strategy, btw.) In an completely free system market forces will, eventually, correct any imbalances. However, in the mean time, people can be hurt by such volatility. The star rating system is, I believe, the throttle of the trading system in Elvenar, but, as I've said, I thinks it's not needed and too artificial....but that's must my view.
Finally, you might note that as worlds progress they go through stages. Imagine you are one of the first player to produce sentient goods on your world. Suppose you are smart and have a lot of resources to "throw" at sentient goods. It is, at the very beginning, possible to "corner" the sentient goods market, but the duration of such a "cornering" would be relatively short as others begin production. In other words, in the face of a constantly growing supply it would be nearly impossible for any player, or even group of players, to sustain such a thing for long. Especially since you can ignore the markets completely and build the necessary supply chain for yourself via your own mfrs and those in your fellowship.
Just my comments.
AJ