“It’s my money, Jake! If you want to bid at the auction, use your own money.”
“I’m Human, I don’t have any money.”
“It’s not my fault that your species decided to abandon currency-based economics in favor of some philosophy of self-enhancement.”
“Hey, watch it. There’s nothing wrong with our philosophy. We work to better ourselves and the rest of Humanity.”
“What does that mean exactly?”
“It means… it means we don’t need money!”
“Well, if you don’t need money, then you certainly don’t need mine!”
The exchange between Nog and Jake Sisko from the Star Trek: Deep Space Nine Episode “In The Cards” provides an excellent example when scarcity is suddenly encountered just outside a so-called post-scarcity society.
I enjoy how Chuck Sonnenburg reviews the episode in question:
There is always some manner of inconsistency throughout the Star Trek canon regarding their ecomomics, and when they do insist they don’t use money, currency, a medium of exchange, it’s usually done with no small amount of pretension and preachy tone. On occasion they take the series where the setting is on the border between different societies to indicate money exists, albeit without much indication of how or why. A mineral of some sort is apparently the medium of exchange between different space-fairing societies, but a male adult from the planet earth, that chooses to live among them, subscribes to a philosophy that leaves him incapable of buying things from civilizations outside his own.