I like this! I feel like there could possibly be a tiny reward (not gralats, or anything that encourages boosting) for when you are rated good, similar to how if someone applauds a message you have left in Dark Souls you regain all your health - perhaps a stat in your profile?

The rating should be changeable to to discourage scamming; if someone is saying they are offering 100g per rating and they do not follow through, those that have fallen for it can simply change their rating from a like to dislike.