But the show is pretty nice about it, and even gives one dude a puppy in exchange for his unwanted gift card.
Every year around this time, Ellen DeGeneres catches audience members who attended her "12 Days of Giveaways" selling their unwanted gifts on Craigslist.
Of course, the comedian doesn't go around busting these unsuspecting people herself. She has a team of trusty employees -- including her writer, Adam Yenser, and someone dressed in an absolutely absurd reindeer costume -- do the dirty work for her.
"You'd think that people would learn by now and stop doing this, but they have not," Ellen told her audience on Thursday's show. "So once again, I set up a sting operation. We emailed them and told them we're interested in buying their stuff -- but really, it was my writer, Adam, along with Comet and a camera crew."
Adam, Comet and Ellen's camera crew then proceeded to flag down a man trying to sell his mattress, a mom giving away her daughter's trip to Cancun, a woman looking to pawn her big-screen TV, and a dude trying to trade a gift card. That lucky guy got a puppy instead -- although we can't quite believe they let him keep it after the camera stopped rolling.