In subsidized commerce, a local government (or a group of several worlds) will agree to subsidize the construction of a commercial starship in return for its servicing an established route. Ideally, the route will be a profitable one, and the subsidy can soon be ended. But, even without profits, the route provides a channel for interstellar trade, producing markets for resources and finished goods alike, and acquainting the peoples of all the worlds with the higher technology or better quality that is possible. Whether this makes the people ambitious to duplicate the artifacts by their own means or simply makes them disheartened depends on the people themselves.
Typically, a subsidized merchant will establish a route which will attempt to guarantee profits. Individual ports of call may not always provide sales at high margins, but overall on the route, sales can be expected to produce reasonable income.
For example, a route may begin with an industrialized world where manufactured goods may be cheaply procured. The first port of call could be a nonindustrial world, one which provides an excellent market for the manufactured goods. That world could export raw materials such as radioactives or textiles. The ship then jumps to a rich agricultural world and sells those goods while buying agricultural products. The ship would then make a return journey, again buying goods at low prices, especially those in high demand at the next world. The route needn't even be profitable at each port of call. Sometime, goods might be picked up along the way with the intention of selling them farther down the line, where the captain knows that there is a market.
Finally, the ship can always fall back on carrying cargo and passengers if no worthy cargoes are found.