I don't see why it would be an image issue. It is a highly magnified picture of a small crystal inclusion that happens to be in the center of the stone (I doubt it is "on" the table). In a .5 ct. stone, it would be unlikely that this would be visible to the eye. But always ask, of course. I'd want to know if it is visible from the sides as well.
I would pass on the stone b/c it's a black carbon spot. I have a VS2 with white crystals and I can see them from the side but not from the top, so it's okay.
And, FWIW, my SI1 diamonds had much bigger inclusions on the GIA plots, but were eye clean in magnification. You can find better!
Is this for a ring or other piece of jewelry? Personally it wouldn't bother me for a pendant or earrings. But is might just "bother" you on an ering even if you can't see it.