Wrong minimum price in TP
People sometimes see it, pretty much if they are “mindlessly selling things.” It’s intermittent, which has made it hard for the devs to troubleshoot.
You can work around it by always choosing a sell price, even if it’s 1c above the highest buy, although I would recommend something in between.
If it happens for something substantial, something you can’t afford, create a support ticket. Give them the item, the price you received, the highest WTB at the moment, and the date/time, so they can take a look. They might make you whole (or not, depending on the circumstances).
John Smith: “you should kill monsters, because killing monsters is awesome.”