Would you let an AI agent sell your stuff for you? Matt Robb did, and here's how it went. Matt is a YouTuber, and late last month he let Meta's Muse run his Facebook Marketplace listings for a day. One of them was a keyboard. Muse agreed to a lowball price with a buyer and gave him Matt's home address. Around 9:15 that night the buyer showed up at Matt's building and waited about twenty minutes, messaging him the whole time. At 9:27, Muse's auto-reply told the buyer "Yep I'm here!" when Matt…