At work we have a online bulliten board in which you can sell stuff. I logged on today and saw something interesting for only $75 (this would be slightly under priced). Well I call the guy and buy it and arrange to pick it up tomorrow.
Wait thirty minutes when the guy emails me that he has since had another offer in which he was offered $100. "Sorry" for the inconvienence, but would I like to bid.
No thank you, and you just sold the only thing you had that was worth anything in this world for $25.