Currently I see an imbalance on all 4 servers I play on, soap being in high demand and bismuth dropping in value.
Today the soap guys will readily find fair trades (or even better) to pick whenever they need them, while producers of bismuth hardly get fair deals und usually have to accept a loss of 5% to 10%
If I understand the Merchant mechanic correctly, and if we had it today for sentient goods, soap producers would readily find fair trades (nothing better) started by other players whenever they need them, while producers of bismuth find no trades waiting, and instead have to pay for Merchants and wait until their next login for their return to trade more, thus being limited by the tradable amount. Note that only the bismuth players would be limited (and exact amount depending on login frequency) while the soap players would not be.
I'd REALLY REALLY rather take the 5% losses than a trade limit for only a part of player base.
(This would not be a problem if produced and needed resources were perfectly balanced, but honestly I do not believe this will happen. Even without things like the current dust manufactory upgrade costs for levels 28 to 31 being off balance, there are things like the spire set with unbalanced production)