That's the basic problem with this feature. I have ratings disabled (removed from the templates).
Here are some queries you could try:
SELECT * FROM w3t_Ratings WHERE R_Type='u' AND R_Rating='1'
SELECT * FROM w3t_Ratings WHERE R_Type='u' AND R_Rating<'3'
SELECT * FROM w3t_Ratings WHERE R_Type='u' AND R_Rating='1' AND R_What='Xyz'
In the last one, Xyz would be replaced with a username whose ratings you want to check. R_What is the user being rated, R_Rater is the user who did the rating.