I am buying a bike from eBay and before I bid on it I just wanted to know what you though about one of the pictures. The bike is carbon and it looks like some paint has come off. What do you think about the picture? Thanks.
As others have noted it can be difficult to assess damage for carbon frames in general, and it is especially difficult from only a photo. That caveat aside it looks like a superficial paint chip, the first layer of carbon (which is typically non-structural) appears intact which is a good sign.
The damage is on the lower drive side chain stay so it might have been from a shoe heel strike. That, said it could have been due to something else like a crash. If you do purchase make sure to inspect this area further. You can tap in the area to see if the tone suddenly changes, and you can try squeezing to see if it is weaker there. If either of those tests show a difference I would treat the frame suspiciously.