Depends on the part. I bought a used bike last season that had a lot of carbon parts. Kept the Campy wheels and SR parts, but replaced the seatpost, stem and bars with new aluminum. I'm sure they're fine, but I ride a lot of long distance, and your ride is over when one of those fails. Carbon FD cage broke so I replaced it with the aluminum cage from a Chorus FD. I bought a used Easton EC90 sl crankset this season and it's been fine.