Well now I'm not convinced that's rust at all - seems more like a stain.

Ah yes, the old "some rust" pitch. A fine addition to any collection is this rare folding razor shaving knife...

I wonder if the seller added a picture of the other side of the blade as well? If so, why? Is it Sheffield, Solingen, or Eskilstuna steel? Things to ponder on a fine afternoon where the air is thin and it only takes half as much alcohol to get a buzz with lunch.