I would most likely pass on that gun. If the barrel has the shroud on it it looks like the shroud has slid foward. That should be an easy repair but why chase trouble?
If thats not a shrouded barrel then it really has problems. Like sombody removed the barrel and didn't get it screwed back on all the way.
It's hard to tell from the low quality pictures but it looks like it's only the sight ramp base that was machined a little short (cosmetic only) vs. the barrel not screwed in all the way. In fact, looking at the other pictures the "gap" does not show. It may very well just be a light reflection. I would ask for a better picture or ask the seller if the gap actually exist before condemning it.