Most of these are scams. Email the seller and get a Serial # off the box. Then call Apple to see if it is a real #. With the # they can tell you when it was sold and who sold it. I'm not saying this one is a scam but there are plenty of them going around. I seen one on there this morning claiming to be a 1GHz G3.
When did you sell your iBook? Was there anything special about it that drew that kind of price?