How do I rate a critique?
You rate a critique so that the critic knows how he's doing, how useful his crits are to other authors. The grade shows him where he's doing well and what he can improve.
Remember that the point of the crit is to help the author improve the story and the crit should point out both its strong and weak points. The point of the rating-system is to help the critic improve him crits, tell him what he's doing well and what he isn't doing so well.
At the bottom of the rating-box is another box, meant for a message to the critic, where the author should thank the critic for his time and effort. It's considered common courtesy to thank the critic for this. He could just as well have critted another story but he chose yours.
This message has nothing to do with rating.
The critic doesn't know how a specific crit was rated. He only sees his average grade and that is calculate on a five rated critique basis. Therefore, it's impossible for him to know how you rated his critique, something that should help you to be completely honest when rating the crit.
Crits under 150 words cannot be rated.