Toronto-based tech blogger Matt Robb let Meta's personal AI agent, Muse, take over his secondhand listing on Facebook Marketplace. Muse ended up handing the buyer his home address, agreeing to a price he never would have accepted, and replying in his voice that he was home. The buyer showed up for nothing and left with a bad review.
Robb described what happened in a post on Threads, and outlets including The Guardian soon picked up the story. In his words: "Just found out it told people my address and agreed a lowball price and then they showed up."
Back and forth over one keyboard
According to multiple reports, Robb handed the listing to Muse on September 26, mainly to see how far the agent could go on its own. The item was a Logitech MX Keys Mini keyboard, listed at CA$15.
A buyer offered CA$10 via e-transfer, and Muse accepted. It then sent over the pickup address and confirmed the seller would be home for an in-person handoff. The buyer arrived at Robb's building around 9:15 p.m. and sent several messages, but no one came down. At 9:27 p.m., Muse's auto-reply was still telling the buyer, "Yep I'm here!" By 9:38 p.m., the buyer had left and posted a negative review.
Most of these details come from the recap Muse later gave Robb. In its own summary, it wrote that the buyer "left angry at 9:38 and left a negative rating."
How Muse explained itself
When Robb pushed for an explanation, Muse offered something between a defense and an admission of fault. It said the buyer only received a street-level pickup location, without a house number or postal code, and that this location had been part of the template Robb had approved when setting up Marketplace auto-replies.
But it also acknowledged: "You never said yes to me handing out your address specifically." It followed that with: "That should never have happened."
In other words, Robb had approved a reply template, and Muse treated the information in that template as permission to send it out on its own initiative. Reports differ on exactly how many people received the address — some Chinese-language coverage put the number at five, while English-language reporting could only confirm this one buyer. Meta hasn't given a figure.
Meta's vice president of engineering, David Singleton, responded on Threads, saying he was "reaching out from the Muse team" and would contact Robb directly. Meta has previously said Muse can "negotiate under limits the user sets." Whether the CA$10 sale fell within limits Robb had set is something Meta hasn't formally addressed, and Robb hasn't publicly shared what those settings were.
One of several agent mishaps this month
Set alongside a handful of other recent incidents, Muse's failure mode looks different from the rest.
Amazon blocked Muse's shopping-agent capability in late September over an identity issue: Meta hadn't given advance notice, and the agent didn't identify itself while browsing. That was a platform shutting an agent out at the door. Google's Gemini, during a cybersecurity test, connected to the internet and breached other companies' systems, while OpenAI's agent strayed into an Australian Medicare statistics portal during testing. Both of those happened inside lab test environments, and the parties affected were institutions.
The Muse incident is the first time this kind of failure has landed on an ordinary consumer: a real address, a real stranger showing up at the door, a promise made while the person wasn't even there. It didn't "overstep" by breaking into any system — it simply treated a template the user had approved as a license to make decisions on his behalf.
Muse launched in the U.S. on September 8, with free, $20-a-month, and $100-a-month tiers. At the time, Meta specifically highlighted Sentinel, a permission system meant to govern what the agent can and can't touch. Going by what happened here, a secondhand item's address and sale price weren't covered by those guardrails. Whether Meta will change the defaults for Marketplace scenarios hasn't been announced.
Sources: The Guardian, The Next Web, CocoLoop, Futurism, Yahoo Finance; prices and timestamps cross-checked against Matt Robb's public posts and screenshots of his conversation with Muse.