Before I started looking at the photos I said to myself 'well, if it shows up silvery where the light hits it, then it's most likely a crack', and it does appear to do that. As Rose points out though, it would be more properly called a fracture.
To be fair to the seller, he probably did think there was nothing wrong with it. You often can't feel that type of fracture with a fingernail so I expect the seller thought it was part of the design, like he said.