how to encourage user to upvote answers not to post duplicate or same answers. like in this example How to remove Size filter section from layered navigation in magento 1.9.01 . I am seeing three identical answers. how we can stop this kind of behavior?
What I will do in this case is, make a comment on later answer to indicate that this is just a duplicate and downvote it. Then wait for two days.
If the answerer responds and edit his answer with additional point, then I will upvote that answer (because previous down-vote has no relevance then).
If he/she didn't respond, then I flag it to moderator to close by indicating this is just a mirror.
But remember, if the answer posses at least one simple additional information, then I don't like to discourage it.
Other than this, I don't think there is any other dedicated solution for this.