Here's the case.
First somebody gives an answer as comment.
Then another one (me) marks the question as exact duplicate.
Then another SO user posts as answer the answer from the duplicate (and the comment) without adding anything.
My purpose here isn't to rant against a specific user as it's possible he didn't even see the comments and that's a frequent situation but to learn what we have to do in this situation, apart using our precious rep points to downvote the answer. Should we flag ?