‘'There’s a certain amount of liquidity that these large sellers inject into a marketplace that can be very helpful for the marketplace to grow rapidly,'’ Arun Sundararajan, a professor at New York University’s Stern School of Business who studies the sharing economy, told me. The competition should also help drive down costs, which helps consumers. But these marketplaces, he added, must ‘'balance the short-term accelerating their growth while also maintaining the quality, and in some sense staying true to what their consumers are looking for'’ — which might be freedom from big banks, or the stultifying sterility of budget hotels.

Still, commercial operators seem to appear wherever the opportunity arises. Juliet Schor, a sociology professor at Boston College who is studying the sharing economy for the MacArthur Foundation, said she discovered evidence of ad-hoc temp agencies on TaskRabbit, an online market for farming out errands and chores. For gigs like copy-editing or proofreading, she said, people who rate highly on the site and get a large volume of requests sometimes subcontract their work to others, taking a bit off the top for themselves.

Getting ahead on Airbnb is much more simple: just sign multiple leases in desirable locations. Of course, that requires upfront investment and financial savvy. But once it’s up and running, an Airbnb rental network can become seriously lucrative. One operation of 272 listings booked $6.8 million in revenue from 2010 through June of this year, according to the attorney general. The economic forces at play are similar to what the French economist Thomas Piketty discusses in his recent blockbuster book, ‘'Capital in the Twenty-First Century,'’ only in miniature. In a slow-growth economy, Piketty argues, wealth delivers better returns than labor, so those with wealth to invest in things (like, for example, rent-earning apartments) will tend to get wealthier; those without probably won’t. Listing a spare room on Airbnb might keep you current on your always-climbing Manhattan rent, but real entrepreneurship (as always) requires real dough.

As Schneiderman has put pressure on Airbnb, large operations have been disappearing from the site. But it still derives about one-third of its revenue in New York from users with three or more listings. And these Airbnb pros have taken up arms. Another New Yorker, a 49-year-old entrepreneur (who also insisted on anonymity), got his start on the site after shareholders pushed him out of the information technology company he had founded, leaving him without a source of income. ‘'I would have been dead,'’ he said.

But after renting out his apartment on Craigslist and through word of mouth, he signed up for Airbnb in early 2011, with a plan to make short-term rentals his full-time job. He signed leases on former factory spaces in Lower Manhattan, renovating them and listing them on Airbnb. At his peak, he said, he managed 12 listings and hired a team of cleaners, greeters and handymen to keep his scatter-site hotel operating. His relationship with Airbnb, however, turned sour when Schneiderman sought data from the company about operators like him.

Now, he is leading a group of users suing Airbnb to prevent it from handing over the information. The group’s name embodies that vast gulf between Airbnb’s radical promise and its reality: New Yorkers Trying to Make Ends Meet in the Sharing Economy.

And who would want to stop a man with 12 apartments from making ends meet?