I was thinking of something like, if a Mod infracts someone that the post automatically says "This post has received an infraction" once you infract them, this way it gets rid of extra spam reports of the same post that was already infracted.
I think maybe a little sign, or a message at the bottom of the post saying 'Moderation notice: This post has been infracted'. Although, if you do infract somebody, you could always write that little notice yourself.
...or just make the little red square visible to users.
I think it would be better to just reject/automatically archive reports for posts that have already been deleted/infracted.

