One of the most inspiring aspects of Gene Roddenberry's Star Trek franchise is that in the 24th century, the galactic economy will no longer be rooted in democratic capitalism. It will exist on a meritocratic system, where instead of remuneration for services rendered, Federation citizens will go into fields for the betterment of their species. The invention of the replicator ensured no Federation citizen would go without their basic needs, thereby eliminating the need for currency to acquire material goods.
That being the case, we still see Kirk talking about paying miners for lithium, and Doc McCoy trying to pay some sort of currency for a ship in Star Trek III. So how exactly does the Star Trek economy work? Star Trek: The Next Generation stated that Earth had long since done away with money, yet features Picard offering to "buy" dinner. Set phasers for skeptical, and read on for 10 ways that the Star Trek economy makes no sense.
While there is no currency as we consider it today in TNG, there was a form of it in The Original Series. In The Search for Spock, Dr. McCoy tries to get a ship outside of the Federation and money is discussed very seriously, but it seemed the further away from the bureaucratic center of the universe, the more Federation credits are of no value.
By the time of TNG, even Federation credits aren't in circulation. Which makes it odd when Captain Picard tells members of his crew he's going to "buy" dinner. It's not explained if this is a holdover colloquialism or refers to some different currency we have no concept of.
9 FUNGIBLE ITEMS
Given the economic system in place during TNG, when every material good is able to be replicated instantly, there are still things that are not fungible, and cannot be replaced or exchanged for something identical or similar. This could mean property near a city center (of which there could only be, by design, a finite amount), or the family-owned Chateau Picard.
Due to the fact that a WWIII level catastrophe altered Earth's former economy (and very survival), forcing surviving inhabitants into a post-scarcity existence, there will always be certain assets that make that sort of existence futile in the future.
According to TNG, money doesn't exist in the Federation. There isn't a need for it, because replicators can provide anyone with whatever material thing they might purchase with it. Those outside of the Federation (like the Ferengi) still use currency like gold latinum, however.
In an early episode of TNG, a stock broker is unfrozen from cryogenic stasis and finds himself aboard the Enterprise-D. He doesn't understand what the people of the Federation pursue if not monetary gain, and therefore stability and success. Captain Picard explains that service to one's species is now the ultimate goal.
7 DISTRIBUTION OF WEALTH
Most of the human colonies that are encountered in Star Trek are small, implying that humans like to spread out and not be restricted to known inhabitable planets like Earth. They are often content to lead simple modes of existence, focusing on art, science, husbandry, and farming.
There are rarely wealthy "humans", simply humanoid aliens. Often they are outside the Federation, where a stratification of power is directly correlated to wealth distribution. It would be almost impossible for anyone in the Federation to be or appear "wealthy" in the sense of the socially elite, as the pursuit of such would be considered petty.
With the onset of replicator technology, material things cease to be rare. Now instead of one Mona Lisa in the universe, there could be hundreds of thousands. Where once the market decided the value of things, not it's left up to individual people.
Perhaps the hassle of owning the only one of a certain item is worth giving up a currency-based economy. But certain material objects from before replicators seem to be considered priceless, such as some of Captain Picard's antiques/artifacts, or those that Vash the treasure-hunter pursues for well-paying clients.
The theme of self-actualization is salient in the Star Trek franchise. Money has been abolished on Earth, and without money, there is no external motivation. Replicators allow for everyone to have their basic needs met, so every Federation citizen on Earth can now pursue goals that improve humanity.
Captain Picard explained that Earth had outgrown its obsession with wealth, and humans were now free to pursue self-actualization. But how do you allocate finite resources to the needs of humanity, which can be infinite? And what about the unwanted but necessary service positions that must exist, even as Federation citizens are pursuing their dreams of becoming artists and scientists?
4 SOCIAL CREDIT
It seems that the Federation functions on some level with a social credit system. An unskilled worker can't simply obtain a job as a carpenter any more than a student that flunks Starfleet Academy can serve aboard the Enterprise-D. So skills are still desirable to achieve postings and positions, even if they no longer garner a certain paycheck.
Without a paycheck as one's primary motivation, then social standing must be given equal if not higher importance. If it isn't the wage one earns aboard the Federation flagship, is it for the distinction and the glory? If that were the case, wouldn't everyone want to be a Commander Riker or a Picard instead of a lowly crewman?
National resources and industries in TNG seem to be under the purview of a variety of governing boards and bodies in the Federation. But what of property ownership? Do families like Picard's get to have their French lands grandfathered into the Federation? Dr. Crusher's family estate?
If a person has an apartment or a home on one planet, but their vocation causes them to split their time between each, how is their domicile kept theirs? Who stops it from being taken over by someone else after a year of non-use? What would have to be "exchanged", if not currency, for an entire dwelling to be considered the private property of someone else in the Federation?
2 PERSONAL TABS
In the very first episode of TNG, we see Dr. Crusher ambling about the promenade on Farpoint Station, shopping the wares of the local merchants. She makes a purchase of some bolts of fabric, and asks that the vendor bill her account on board the Enterprise.
On a separate occasion, when Captain Picard is going to Risa for a little shore leave, Riker asks if he'll pick him up a horga'hn. In both of these cases, objects are desired that could be produced by a replicator, but a transaction occurs and the items are acquired with the use of a credit system/personal tab. It's never stated if this is a common method of exchange for everyone in the Federation, or simply Starfleet personnel.
If gold once backed the value of our own paper currency, what might back the Federation credit? It's clear the Federation has to use some form of currency to barter with non-Federation worlds, such as in Mudd's first appearance in TOS. Kirk explains to a mining foreman that he's been permitted to pay a high price for the lithium crystals that he needs for the Enterprise.
In Deep Space Nine, Commander Sisko explains how he once used all of his "Transporter Credits" to get home for the holidays from Starfleet Academy. If these sorts of credits aren't back by currency, are they backed by resources produced in Federation Space? Does each individual get an allocation of those resources to use according to their needs?