I've read a lot of criticism about the bike blue book having some unrealistic valuations. The very few I looked at didn't match what people were asking or getting. One way to see what other people are asking for your bike is to use Ad Hunt'r - Search ALL of Craigslist? and more! and enter "Cannondale Caad10" in the search box. There are pages of listings on CL across the nation. It is pretty rare to see any listed at prices below $1K. Show that to your friend and it may change his mind.