My 30 Second story:

My roommate Kevin was out at the grocery store getting some eggs. He was stopped by a middle aged man down on his luck. He was selling a surround sound stereo for $600 on the side of the road. Kevin said he would buy it for $400. So money was exchanged and Kevin brought the system home. He was thinking of selling it on Ebay, but when he looked at the prices online, he found out that the stereo was only worth three hundred dollars. Miserable he came to me to ask what he should do. I bought the stereo system for $200. I win.