I've had a few flags declined from time to time that make we wonder what the UI looks like for a moderator when reviewing flags? The odd fat-finger aside I suspect a few things that throw some reviews are:
Is it obvious that a flag was raised on a previous revision of a post?
If multiple flags of different types are raised, for example NAA and spam is it clear that handling it as NAA will decline spam flags?
I noticed when posting this question that What exactly can moderators see when one raises a flag? came up as related but I'd like to know the UI and workflow if possible. I realize moderators may not be able to describe it in detail because of the moderator agreement, but assume it's not really top-secret so if not perhaps a team member could provide a redacted version of things.