amti, I have never seen a crack like that either, however, that was my first reaction.
I feel it's very important, especially when purchasing pearls on line, to ask for photos of the actual pearls you will receive. Buyers should inquire about flaws, what kind (pin prick, scratch, etc) and where on the pearl they are located. Ask for pictures of the flaws, as well as photos of the pearl under different lighting conditions. I would ask to examine other pairs (and I agree with the others, swapping out ear wires is really not a big deal). I would hesitate trying to match the one good pearl, because that may be more of a challenge than looking at a completely different pair.