Does Job 7:9-10 state that ghosts don’t exist?
In my opinion, no. I think it means that the dead can not come back to earth, to live. And it recognizes that most people can’t see the spirit world.
When Jesus first appeared after being crucified, the apostles thought he was a ghost…in that sense, it suggests they knew what a ghost was, and there was a word for them, so its likely ghosts had been seen before(whatever they may be), although Im not sure a ghost in those days is the same thing people report seeing today, but maybe they are?
They didn’t know about eternal reward in heaven (or eternal despair in hell) in that time. Rather, they believed in the “abode of the dead”, where all went following their lives on earth. The Jews called the abode of the dead “Sheol”, and Greeks called it “Hades.”
In Job 7:9-10, he’s just affirming that no one can leave Sheol and return to (normal) life on earth: in other words, you get one shot, and that’s it.
And, of course, since ‘death’ was considered one of the ways that God was understood to punish sin, Job is lamenting the ‘fact’ that it seemed that God was punishing him for something, since his days seemed to be coming to an end (although, for the life of him, Job can’t figure out why he’s being ‘punished’).
Rather than about ghosts, I think the passage is about bodily resurrection from the dead. There have been some Old and New Testament exceptions, of course, but generally the bodily resurrection won’t occur until Christ’s Second Coming.