Examine every inch of frame,any dents or imperfections no matter how small,steer away ,I have a frame that I've had from new being mended as I type ,just some thing off the road hit the rear stay,I just tap around the mark and the sound changed ,crude track test but it works,carbon tends to deteriate in crash cases from the in side out,I even seen mock up reports from frame makers,and then break ,defiantly buyer beware