I wish to go for this before, but with what you explained, I have a second thought, it can be possible that this can make other members on this forum that are not reporting now to start to report posts and many good posts may be reported which can become a problem for the moderators.
If posts are often reported effectively, I think reporter badges should not be done, theymos can just be making yearly post about good reporers and how they all appreciate their efforts.
Shouldn't be too much of a problem. They need good reporters to get the badges, and if they're reporting inaccurately they aren't going to get them. You could counter this problem by deducting bad reports from the good reports a user makes. The only issue I see with it is it could be short lived. Users will have the motivation in the beginnings to get the highest badge, and then unless we keep adding badges users will stop once they've reached he highest badge.
But, yeah; users reporting inaccurately shouldn't be a problem. We've got enough moderators to deal with it, and it doesn't really effect the moderator much to mark a report bad, instead of good. There might be a few select users that could become problematic if they're just reporting everything, but again that's just counter productive.