For me reviews are all about expectations. If the girl delivers all of the services you have chosen from her Likes List, has a good attitude, is enthusiastic and all the admin ie. comms, venue, facilities, punctuality etc then you would be hard pushed not to give a positive review. Doesn't mean it was the best punt ever but you got what you expected to get.
If any of the above are not delivered, it does give the punter scope to give a neutral review. Clearly multiple 'failure to deliver' might incur a negative review. That said it might be sufficient if, say, she had a terrible attitude, or was completely unenthusiastic, to give a negative review based on that alone.