How to tell if a carbon frame is damaged or if the paint just has stress cracks I am looking at a carbon framed road bikethat has me concerned.On the topside of the bottom bracket,drive side there is a very small hairline crack in the paint.The seller states that it has been there for two years with no change.He was told by the dealer that it is just in the paint and a fairly common occurence.Anyone else experienced this?It is a three year old cervelo.The crack is 3/4 inch long and you can't feel it with a fingernail.
Markus Storck, lead engineer and owner of German carbon frame powerhouse Storck Bicycles, told me at a conference about 3 months ago that the best ways to tell if a frame is cracked are movement and time.

Movement, because a crack will flex if it's through the paint into the carbon, and you put pressure on the center of the crack, and time, because a crack will grow with time if it's more than paint.

If you are even halfway concerned with a crack, don't buy the frame.

It's just not worth the risk, unless you can afford to be wrong about the frame's ride-ability.

I hope that helps.