You sold an old couch on Facebook Marketplace and got paid through Venmo, or you sold last season's clothes on Poshmark. You thought that was the end of it, until an unexpected tax form arrived in your mailbox: a 1099-K. What is it, and do you actually owe taxes? Even if you're not running a business, these forms can land in your mailbox, and with them comes a new set of reporting responsibilities. Understanding how Form 1099-K works, what the IRS expects, and what's actually taxable can help you stay ahead of any surprises during tax season.