Looks to me like the fork has crown supports between the blades. The apparent damage seems to be on the supports, also, suggesting to me that the marks might just be dirt or debris, of some kind. Look at the other pictures on the listing and you will see a similar mark near a drop-out...



Of course, I could be wrong. Also...

If the seller is uncooperative now, walk away is all I can say. The frame might be just fine, but the seller might prove troublesome