Alien Zoo Ship

Nicholas van Rijn's men have captured an alien zoo ship and want to communicate with its crew who, however, have destroyed all evidence of their identity and are hiding in plain sight among their exhibits. When it is realized that the ship synthesizes food even for the crew, van Rijn comments:

"'...maybe here we find a good new market. And until they learn the situation, we can charge them triple prices.'"
-Poul Anderson, The Van Rijn Method (New York, 2009), p. 578.

Are triple prices, even just temporary ones, ethical? I am not an expert in capitalist "morality." (Despite my sneer quotes, van Rijn, unlike some merchants of the Polesotechnic League, does have morality. He regards nuclear bombardment of a hostile planet as not only economically wasteful but also morally wrong, a guilt that would kill the League.)

Even more interesting are the technicalities of the zoo ship. The crew has emptied the ship of its air although, of course, each "cage" has an internal atmosphere. But is the air in the reserve tanks similar to that in any of the cages? There are no reserve tanks. Instead, an adjustable catalytic manifold renews air and chemosynthesizes losses from a store of inorganic matter. When, as the hiding zoo keepers must hope, van Rijn's men give up and depart, they will open their cage to let out some of its air so that the chemosynthesizer will then fill the ship with their preferred atmosphere. Pretty smart stuff.

Some of the exhibits are clearly just animals, incapable of building a spaceship. For the suspects, the chief engineer has constructed equipment to assess gravity, temperature, illumination, atmospheric composition and pressure etc in each cage but it takes time to translate dial readings into data. Each cage is metered but of course the meters are incomprehensible. Meanwhile, can pure detective work identify the zoo keepers? Van Rijn, who seems merely to eat, drink and idle, also thinks very hard.