Scamming
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Just when I had paid to enter the city and finally get to see what the true purpose of this trial was, suddenly, we were called out…
Or well, I was called out.
"Oi, who are you trying to scam here, you fuck?" wondered the green guy.
His attitude instantly gave a sudden shift as they realized that the crystals had no "starlight energy" apparently these things weren't just used for coins, but were somewhat mined, perhaps in the Asteroids? And it was also the damn fuel for their stuff! So it isn't really a steampunk world, its just the appearance of everything.
"Scamming is a crime, sir," said the rusty robot. "These jewels are not real, they're replicas. Very well done but lack the starlight energy they contain inside. Which is essential to power our technology… Where did you get these?"
Well, that tells me everything I need to know.