Newer writers are always terrified that their story, play, screenplay, novel will be ripped off by some evil crooked producer or publisher. And such things do happen. There was a headline yesterday that accuses a famous director of copyright infringement. I don't know the particulars. I do know such things are actually fairly rare.
What few people think about is looking at things from the other side of the desk. On the anthologies I've edited that were not invitation only, most of them have had at least one submission presented to me that was not what it seemed. If it's a no reprint anthology, I'll usually get at least one story that's been published somewhere else. The most blatant thing I ever got was a short story by a major 19th century author billed as an original story some guy sent me.
Well, on the forthcoming Martian Anthology, which was not restricted to original stories, I got one anyway that the cover letter said it was original and never published. Well, a quick computer search found it in a magazine from four years ago. So, if that writer had simply disclosed it, I would've accepted it. Since I was lied to about its history, I rejected it. Are we having fun yet?