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john, when u flag a post by account with higher rep, u only have effect on its reward, not on its rep, and since this comment already had 0 rewards, u just wasted ur voting power.
Keep to only flagging accounts with lower rep than urs, and to flagging posts by undeserved reward by anyone.

Thanks for your concern, but the flag was not intended to have influence on reputation, it was a message to the spammer that his comment was not well received. As such it also wasn't wasted.

Before this downvote was issued, the commenter's profile was checked.