Unfortunately there's no set answer to your question as the answer depends entirely on the 2nd hand bike in question.
I was wondering when you would start chatting $#[email protected] about my posts again... You were chatting $$#@[email protected] about everybody's elses posts except mine!!!
Ignore the post-bashing posts of Aliens, he is probably gone mad from all these sultry images he paints in his alu-forks...
Yes basically I had some problems with the syntax of the question of the Original Poster and posted something "relevant" to communication problems (with an evil twist I so like, instead of sultry viking women with aero-handlebars on their helmets like the ones Aliens paints on his alu-forks).
In theory carbon fiber has excellent fatigue damage resistance (not sure about the epoxy resin that holds them together though) so a second hand Carbon fiber bike would be an interesting option, especially since cf bikes are very expensive new.
On the other hand though, if the bike is indeed in good condition and the components are also in good condition, if its not as good as "new" other model then it might not make it such a great deal.
Plus new bikes come with a warranty that might have expired on a second hand bike.