Not that I can help with any on screen evidence, but I do sometimes wonder about the economics of the the federation.
ie: people are going to want to get around but don't have their own ships, and the federation don't have the capacity to move mass civilian population, so some enterprising young engineer applies for three ships to be built that he can use to ferry people from one planet to another. And there's a private venture.
Also, the cabbage grown on another planet is really tasty and they need to ship it around. they won't do it themselves so they contact mr enterprising engineer, and he uses part of his cargo space for shipping cabbages.
All of a sudden it's taking off and there's a fleet of cargo ships that are privately 'owned/used'!
Shame we never see them.
I like the idea that people do things because they love it! It makes me all fuzzy!
I always figured that starfleet ships would ship starfleet cargo around. It would seem unusual to ship around civilian people/things unless in emergencies.