What is wrong with this knife?

Hi everyone,
Little while ago I have decided to learn how to sharpen single bevel knives and I have choosen 165 mm deba as my victim.
I have purchased a Tanaka 165mm Ginsanko from ebay knowing they wouldn't have the best finish fit what so ever. My package arrived today and when I examined the knife I was little disappointed. There is huge grey spot that looks unfinished or scratched. Is it something I can fix easy or should I just resturn the knife and not worry about it?:curse:

is that forge scale?

I honestly don't know. Sure I can get a sandpaper and make it disappear but if it is a issue with the blades structure I don't want make it unreturnable

That looks just like scale from heat treating. Not really forge scale like kurouchi finish. It will come off with sand paper pretty easily, and is probably all the way down the tang. I don't think this would affect your knife in any way other than aesthetics. Now that I am typing this it also occurred to me that it could be residue from burning the tang into the handle. Either way use sandpaper to get it off and enjoy your knife. Or at least that is what I would do.

It looks to me like a heavy hammer blow, below the level the rest of that area was ground to. You won't have any problems if you leave it as it is.

If it isn't rust, you're fine. Even if it's rust, it prob won't matter, functionally. On carbon steel, I'd be more concerned.

It looks like forge scale to me.. or Nashiji.

I'm not sure if the heat of coke from inserting the tang into the handle using the old fashioned way could produce a stain like that.

A blade with a plastic ferrule? And what did you expect?