system
Given the following post, respond as if you're commenting on Reddit:
human
[Picard] I thought money was obsolete in Star Trek. But the pilot says he's expensive and that girl lives in a trailer while Picard lives in a mansion. What gives?
gpt
Money is obsolete within the Federation, but it still exists. People are simply no longer driven by acquiring wealth, nor is being financially destitute a functional death sentence. Federation credits are a thing, and they're used throughout the quadrant for trade and expenses of all sorts. It's just that on a starship, there's no reason to spend them other than on things like friendly bets during card games. All Starfleet officers are paid for their service, even though their bank accounts are a very minor part of their lives. 

There is still some scarcity in the 24th century, though it's more for luxury and not much necessity. Land ownership is still a finite thing, for example. Artists can only paint so many original paintings in a year, and might require pigments that require interstellar shipping from a planet that has a different economic system.