"We [science fiction writers] always wanted to believe in "private sector" space -- hucksters make better characters than a government does."
- Larry Niven

Another nice use of this idea is found in Robert Heinlein's 1941 story Methuselah's Children. Lazarus Long has a problem. What kind of ship could be used to lift one hundred thousand people off the surface of the Earth in a hurry?

He found his answer in a Diana Freight Lines field just outside of Luna City.

...Despite efforts to make the Moon colony ecologically self-sufficient, Luna City still imported vastly more tonnage than she exported. On Earth this would have resulted in "empties coming back"; in space transport it was sometimes cheaper to let empties accumulate, especially on Luna where an empty freighter was worth more as metal than it had cost originally as a ship back Earthside.

They suited up and left the dome by North Tunnel, then strolled along the grounded ships in the long, easy strides of low gravity. Lazarus soon saw that just two ships had both the lift and the air space needed. One was a tanker and the better buy, but a mental calculation showed him that it lacked deck space, even including the floor space of the tanks, to accomodate eight thousand tons of passengers. The other was an older ship with cranky piston-type injection meters, but she was fitted for general merchandise and had enough deck space. Her payload was higher than necessary for the job, since passengers weigh little for the cubage they clutter - but that would make her lively, which might be critically important.

As for the injectors, he could baby them - he had herded worse junk than this.