Airbnb has taken dramatic action against one of its biggest hosts in Canada, shutting down his account last week and others linked to it following a CBC investigation that found they were listing the same properties under different names, boosting each others' ratings and — according to hundreds of reviews — misleading guests about the state of the accommodations.

But the popular short-term rental company won't say why it didn't warn travellers who had already reserved with Montreal-based "AJ" that he was under investigation and that his listings were suspended as of two months ago, or give them the chance to cancel. Hundreds of people stayed at his places even after he was blocked from booking new guests.

"It should have automatically been an email to me or a phone call to me and say, 'Look, your host was suspended,' or 'Sorry, we can help you find another place or give you your money back,'" said Stacy Lapierre, who booked a decently reviewed "Charming Old Montreal Loft" back in April for a mid-July holiday with her girlfriends.

When the Nova Scotia business owner and her friends arrived, "The floors were disgustingly dirty. There were broken mugs.… The beds were chewed by the mice." She had no idea that at the time, the host, AJ, was actually blocked from booking new guests.

Lapierre and other travellers who dealt with AJ told CBC the fact that AJ and a number of associated accounts operated the way they did, for as long as they did, raises questions about Airbnb's ability to protect guests and detect problematic hosts.

Copy-and-paste reviews

AJ — who gave his full name as Alexander Zakowski — was the No. 4 Airbnb host in Canada by number of listings in a CBC tally from April. When a reporter interviewed him then, Zakowski said his property-rental business mostly offered furnished apartments to Montreal university students, and rented them out short-term during the summer months.

He built his Airbnb profile quickly, joining last year and getting his first online reviews in December.

Those initial guest reviews were encouraging, and by early this year, he had enough positive feedback on his 90-plus listings that he became a "superhost." Airbnb says it's a status reserved for those who provide exceptional hospitality, but the designation is also an enticement for potential guests.

It seems odd in the case of this particular host. Airbnb markets its vision of stays in real people's homes and direct relationships with personable hosts, but people who rented from AJ — including those who spoke to CBC, and dozens posting online — rarely, if ever, say they met him.

When checking in, they would usually get an address and a door code via text and find keys in a lockbox. Calls to the phone number he gave out to guests were generally only answered with a terse text message: "Pls txt."

An Airbnb user named 'Alex' posted the same guest review 17 times on AJ's profile in March and April. Alex's profile photo is fake, ripped from the Instagram feed of British actress Ashley Madekwe. (Airbnb)

Another concern: Peppered amid the online feedback for AJ are dozens of positive reviews from the same three Airbnb accounts. In December, when he was just getting going, more than half of his 13 reviews came from three "guests" named Britni, Alex and Francois. Then in April, May and June, he got 93 thumbs up from those same accounts. They almost always left the same review, too.

"I booked the place for my employees and they were all very satisfied as usual. Will be booking again. A+ host!" Britni wrote 26 times in May alone.

Last-minute switches

Around the same time, AJ's reviews from other guests were turning more negative. "No heated water, full of bed bugs, house had thin walls," said a comment on his profile in May from "Shivang."

There were dozens of complaints about vermin-ridden apartments, foul smells, garbage on the floors, broken windows and glass.

Reviews on the profile of now-banned Montreal Airbnb megahost AJ list a litany of problems. (Airbnb)

Other complainants said their reservations were cancelled last-minute for a variety of reasons (flooding, water shut-off, double-booked, door code unavailable) or none at all, and then they would be switched or "upgraded" to another apartment that was dirty and lacking essentials.

A few showed up to check in but say they were left stranded on the street when no one replied to their text messages about how to get in.

Guy Poulin, who in March had booked a family stay with AJ for July, took notice. He saw that the host of the three-bedroom apartment he'd reserved in Montreal's Plateau neighbourhood had gone from a five-star rating to reams of complaints, he said. The copy-and-pasted comments from the same "guests" were worrying, too.

He told CBC he immediately contacted Airbnb and asked about getting a refund.

Airbnb had apparently noticed AJ's falling ratings, too, because a customer-service agent messaged Poulin that AJ's listings were under suspension, according to screenshots of their chat session that Poulin provided to CBC.

But Poulin said the agent told him he couldn't cancel and get a full refund, because AJ hadn't actually violated any terms of the upcoming reservation.

"Please be assured, your reservation with AJ will be honoured by him," the Airbnb agent wrote in their chat session.

Had he not reached out to Airbnb himself, Poulin believes, he would never have known about the suspension. There was no indication to be found anywhere on the site. In the end, he pressed AJ about all the bad reviews and was switched to another place. Poulin said it was fine.

'It was a joke, basically'

Jana Iyengar wasn't so lucky. The U.S.-based software engineer had booked a summer trip to Montreal back in March and reserved one of AJ's apartments for his partner, two kids and some relatives from Toronto. But he never checked back on AJ's reviews.

Iyengar said that a couple of hours before they were supposed to check in to the "Cozy 2-Bedroom" in the Plateau, AJ texted him claiming the reservation was cancelled, but offered another apartment across town that wasn't on Airbnb. In a pinch during Montreal's peak tourist season, Iyengar and his family agreed to take it.

Jana Iyengar, seen here giving a talk, says he's asked Airbnb for a full refund on his booking with 'AJ' in Montreal last month. 'It was a joke, basically,' he says of the apartment. (Fastly/Vimeo)

"It was insane," he said. The temperature was hitting 31 C outside but the place had no working AC or fans, there were four pillows for seven people, barely any bedsheets, no soap in the bathroom and he couldn't get the Wi-Fi to work. "It was a joke, basically."

Iyengar had also not been told that AJ's listings were suspended more than a month earlier. He said he's frustrated and is asking for a full refund.

New hosts appear with same listings

Airbnb told CBC News it initially suspended AJ's ability to book new guests but didn't disable his entire account, which is why his existing bookings weren't cancelled. It wouldn't say when exactly that happened, but the chat messages with Guy Poulin would indicate it happened by mid-June.

Hundreds of travellers had already reserved apartments from AJ for the ensuing months, however, and their bookings were left intact. Airbnb wouldn't say why it never notified them or gave them a chance to cancel.

A host called 'Barry' became active on Airbnb in June, just as AJ, one of Canada's most prolific hosts, was suspended from accepting new bookings. Barry's profile photo is fake, and CBC traced it to a San Francisco-based web content manager. (Airbnb)

And there's another twist. After AJ was blocked from taking new reservations, 45 out of 58 of his listings that CBC News were able to track were shifted to a new host account called "Barry," with no trace of the hundreds of negative reviews AJ had received. Other of AJ's listings showed up under another new account called "Arvin."

Guests who stayed with Arvin told CBC they experienced many of the same problems as AJ's guests: filthy and shoddy accommodations, double-booked apartments and last-minute switches.

"There was gum stuck on the kitchen floor, there was mildew in the bathroom, the fuse blew in the middle of the night, there were air conditioners that had extension cords snaking all over the place," said Vancouver-area resident Mike McKenna, who booked three nights with Arvin on a family trip to Central Canada last month. And this was at a "free upgrade" that Arvin offered them last-minute that they accepted.

"There were flies everywhere," McKenna said of the place.

Among other issues, 'there was mildew in the bathroom,' Mike McKenna says of a supposedly upgraded apartment his family rented from Airbnb host 'Arvin.' (Submitted by Mike McKenna)

Comments on Arvin's profile aren't much better, with many calling him unresponsive and his apartments awful.

Curiously, midway through July, the same Britni who positively reviewed AJ 40 times in the spring showed up 20 times as a guest of Arvin, and at one point left him 10 reviews in a row. They all said the same thing: "Booked for business purposes. Great as usual. Will be booking future. Thanks."

Records from their bookings that McKenna and two other Arvin guests provided to CBC show that the contact number and check-in instructions were the same as for AJ's guests.

In all, "Arvin" hosted at least 140 people from his first reviews in June through August.

CBC emailed, phoned and texted Alexander Zakowski — AJ's real name — to ask who "Barry" and "Arvin" are, and how his Airbnb listings came to be shifted to their accounts. CBC's questions were acknowledged but never answered.

9 accounts taken down

Arvin's account was still taking reservations in late July, but his listings were blocked as of early August. Barry's account was still taking reservations last week, until CBC asked Airbnb about it.

Both accounts disappeared entirely from Airbnb's platform on Friday afternoon. The company said it shut them down under its policy on "misrepresenting yourself or your spaces."

As of Friday afternoon, the 'AJ' profile on Airbnb — as well as eight others associated with it — could no longer be accessed. (Airbnb)

Airbnb took down AJ's account on Friday, too. It also closed those of "Britni," "Francois," "Alex" and three others that CBC's investigation found had all listed some of the same apartments, given out the same phone number and check-in instructions, and — with one exception — either given or received positive reviews to each other.

Airbnb said AJ was violating its standards for "authenticity" and "reliability," which ban things like having duplicate accounts, misleading guests about accommodations, leaving "fraudulent reviews," being unresponsive to guests or providing unclean accommodations.

"We will continue to take action should this host attempt to re-list these properties," the company said in a statement. Airbnb said it is already issuing refunds to anyone who had an upcoming reservation.

For Montreal Mayor Valérie Plante, the idea that guests to her city weren't informed about potentially critical problems with the accommodations they booked means Airbnb "clearly" needs to improve its monitoring.

"As mayor, this makes me really mad," she said in an interview last week. "It's totally unacceptable. It's irresponsible of these [hosts], but ultimately, the one to blame is Airbnb."

Airbnb says it "frequently monitors host activity to ensure that it is consistent with the expectations of our community and policies."

But guests who spoke to CBC want the company to do more to alert them to potential problems.

"The reason I booked with AJ is not because I like AJ, it's because I trust Airbnb," said Jana Iyengar.

"If Airbnb has lost trust in the host … I certainly don't want to stay with them anymore."

Send any tips on this story to Valérie Ouellet at valerie.ouellet@cbc.ca.