Negative reviews are really usefull to help other punters. Positive reviews often make it harder to see the girl in question as I know to my cost
FWIW I think that negatives are more valuable than positives - the problem with positive reviews are:
a. Everyone is different, what I find amazing, you may find just 'ok', so if I tell you that WG x is the best thing ever, I may be building your expectations up unrealistically
b. Very busy full time WGs can't sustain that level of performance over time. If they see too many punters they burn out. That means you're either going to be in for a long wait to see them, or their standards will slip
Whereas a shit WG who shouldn't be in the job will stay fairly predictably shit, she is unlikely to improve suddenly.