Airbnb disputes that home-sharing has significantly reduced housing for the poor and moderate-income, pointing the finger instead at rising demand and restrictions on building new units. But in recent weeks it has taken steps to comfort alarmed officials, a sign perhaps that these sorts of aggressive steps by tenants are helping sway the debate. Starting in November, for example, Airbnb instituted a “one host, one home” policy in San Francisco and New York as a way to knock out investors who may be collecting apartments to market on the web for short stays.

“We strongly oppose illegal hotels and bad actors who remove housing from the market,” said company spokesman Nick Papas. “We’ve removed thousands of listings from our platform that aren’t right for our community. We are committed to working with cities to address their specific needs.”

Still, with municipal governments lacking the staffing to enforce housing ordinances, there’s no shortage of work for private eyes like Joffe. When he’s not taking pictures of people coming and going, he sometimes poses as a prospective tenant to see if landlords allow short-term rentals.

One case he looked into involved Brian Grzybowski, who claimed in court papers that he and his wife were forced to leave their $2,950-a-month Potrero Hill apartment in 2015 after the landlord falsely claimed they needed the apartment as a permanent residence for a family member.

The unit soon popped up on Airbnb, Craigslist, FlipKey, Zeus Living and Tripping.com, according to the complaint in California Superior Court. Now the Grzybowskis are paying $5,500 a month to live a block away. It’s against San Francisco law to evict someone for the purpose of leasing their apartment for a short term.

Joffe’s job involved inspecting the unit, in the presence of attorneys from both sides, to determine that it was set up for short stays. One finding: it had small soaps and shampoo bottles, as would be found in a hotel room.

The suit was settled in a way that didn’t require an admission of liability, said John Brydon, whose law firm represented the landlord.

San Francisco, with its rising rents and healthy tourism industry, is ripe for “below radar” evictions, said Joseph Tobener, the Bay Area tenant attorney who represented Grzybowski.

“You can get more for an Airbnb than you can for a full-time rental,” said Tobener.

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A study in San Francisco found that neighborhoods with the highest number of evictions in a one-year period also had the highest number of commercial hosts on Airbnb. While there are many reasons for San Francisco’s affordable housing problem, said Kevin Guy, director of the city’s Office of Short-Term Rentals, the growth of such rentals “are taking units off the market that would otherwise be available to people who want to be long-term San Francisco residents.”

To be sure, the study noted the boost the city got from tourists who otherwise wouldn’t have been able to afford its hotels. And for many people, the income from renting couches or extra rooms allows them to afford to remain in San Francisco.

Still, Airbnb decided to cooperate with limits on home-sharing implemented in London and Amsterdam, and dropped a lawsuit challenging fines against people who post apartments in New York that were illegally converted to short-term rentals.