The merchant brigands know the buy prices for commodities at all islands. They pick their destinations using a secret formula that includes distance and price. Merchants will not engage player ships, but may be attacked by players. If the merchants have won any battles along the way, they will sell their plunder (e.g., cannon balls) when they reach port.
Merchant brigands always start at uncolonized islands, but never sail back to them. Merchant Brigands will continue to load and deliver commodities from an island until it is colonizable, taken by a player flag and a fort built. The merchants will also continue to load from an island that is controlled by a BK but not built on (confirmed by OM Hypnos)
Merchant brigands, unlike usual brigands, carry the title <Merchants> instead of <Brigands> on their ship's panel. Merchant brigands also lack the swordfighting icon on their might ring that their brigand counterparts have. Like brigands, they can rank from sailors to imperials. If a player ship defeats a merchant brigand, the players receive a portion of the merchant's commodities in addition to the PoE they would have received from a similarly difficult brigand. Small merchant ships tend to carry valuable and rare commodities while the large merchant ships usually carry fairly common, bulky items such as hemp and fruit.