My better half bought a very lightly used carbon fiber (Crammeroti Quattro) from a friend of his and discovered a crack in the bottom bracket after riding it for a year. Turns out some ham-fisted mechanic had screwed the bottom bracket assembly in crooked and cross-threaded it. The friend raised a stink at the shop that he'd originally bought it from and they replaced the frame, a model no longer made, with an identical new one that they'd had for a few years. The new one has so far not had problems, and was assembled with a lot more care.
It would seem that mechanics have to really know what they're doing with the torque wrenches where carbon fiber is concerned, so buying from a shop that wants to sell you a too-small bike is probably not a great idea. For that amount of money, you want a shop where they care and know what they're doing.