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One guy edited a question to add a possible dupe link at the top. Is this action right? Shouldn't a simple comment+flag be enough?
I considered rolling it back, but he seems to have pretty good rep and I haven't been on SO long enough to tell if what he did is acceptable.
Definitely revert because that is not a thing you do.
If it's a duplicate, you cast your close vote, or flag it. Commenting is optional and automatic at 3k+ rep, but you don't edit it into the post body because Community does that automatically. (If it gets closed, it'll have two duplicate boxes at the top.)
Also, whether it is a duplicate is not up to a single editor to decide; there's a reason closing requires 5 votes.
Yes, you should. That is not the appropriate action for suggesting a possible duplicate. Until it actually gets closed as a duplicate by 5 people, it is only a possible duplicate and the question is still perfectly valid. The only appropriate action is to vote-to-close and list that as the question believed to be a duplicate, which auto-posts the comment. If they don't have that privilege yet, that's what flagging or commenting is for.
Not to mention, once it does get closed (if it does), Community is just going to add another box on top of that with the properly formatted, actual duplicate box.
