People in this thread are nuts lol. They probably want the serial number so they can check with Valve if it was reported stolen. When I bought mine used, people were telling me to get the serial number first for this reason. Now for some reason they’ve switched to thinking there’s some huge danger in telling the buyer the serial number. There’s nothing they can do with the serial number that can cause you an issue, especially considering you’re selling the Deck anyway. Valve knows what serial number was sold to what account, so the idea that they’ll try to report your Deck as stolen makes no sense.