as best i can tell a rating of 8 on appearance equates to a double bagger and a rating of 7 for performance means that it wasn't good enough to go back. the ratings are a throw-back to the days when pre-pubescent romanians got 10's iN gymnastics.

It's all we have.
Developing a comprehensive rating system is not as easy as -Monday-morning-quarterbacking would have one think.
A "Likert" scale is an alternate (but not a very good one for this type of evaluation.
It's easy to criticize. If you'd like, try revamping the system and submit it to STAFF for evaluation.
For now, we have to use what's available to us.

Over-rating is a common problem on this and every review site.  Guys tend to write reviews too soon after the event and while they're still smitten from the experience and the lady's charms.  For most reviewers, just consider a '7' or '8' to be about average, no matter how she did or what she looks like.