I'm developing a website for jobs search. The nature of jobs is that they are coming and going - some published job might be not available just after a few days.
When user trying to access an unavailable job (its link still appears in Google) - I need to show a page saying "this job is not available anymore".
Initially I was displaying regular 200 page saying that job is not available anymore. But as result, Google had multiple URLs leading to the same "content".
In order to improve SEO ranking and avoid penalty for having "duplicate" content, I decided to return "job not available anymore" with code 404.
Now I getting warnings from Google that I have multiple 404 errors.
What is the correct approach to handle a "job not available anymore" scenario?