we don't see her bartering with the merchant
Crusher: "I'll take the entire bolt. Send it to our starship when it arrives. Charge to Doctor Crusher. "
No barter necessary, she simply bought it outright.
Which would imply some type of currency exchanged hands.
But was "no money" a Roddenberry rule? Wasn't it originally introduced in The Voyage Home
The Federation could have some sort of credit system in order to allow itself and its citizens to trade with the outside universe. Within the Federation everyone gets what they want but if they deal with the outside they must provide something in return. Not saying that it necessarily has to work that way but I don't see such instances (another good example is DS9) as a contradiction to the Federation being something akin to a true Communist society (or whatever you want to call it).
And yes, I also believe that it was first introduced in "The Voyage Home", where it could mean anything, really - Kirk could have just meant that they normally used virtual money. But Picard's statements in "First Contact" can't be so easily dismissed.
"Mama always told me not to look into the eyes of the sun. But Mama, that's where the fun is."
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