How to handle article content posted by users with duplicate content

Are the same user posting his/her real estate multiple times (to be on the front page)?
Or are there multiple users posting about the same apartment?

The second one should not be possible, you can't rent/sell another persons property. But I have no recommendations on how to find this by programming, as they create their own content and not appending links to other places. They can just change some text and it will not match the previous apartment.

So you will need to approve everything or hire some staff to look on all incoming apartments and give out warnings/ban people.