Feedback is great to help prove that you are not fake but can't give you an indication of how good the girl is. Feedback from returning customers could be a good indicator, providing they are not fake feedbacks of course. Field reports are better than straight feedback as they provide a insight into the happening within a meet. Until you have met a girl you never know it is always a risk but research can help reduce that risk.
At the same time a girl with no feedback might be the best punt you ever have, yet you would have to take a big risk in finding out. Some punters like that risk as the unpredictability can also be a turn on in its self...
I like to use a potential punters feedback to gauge whether he is a time waster or not and then the language he uses in emails and phone calls to gauge whether I want to see him or not. But feedback can't tell me if the punter was a good shag etc even if the feedback states he had a huge cock etc. Even then that only helps if he goes through AW to begin communication. Again its a risk as to who you are going to meet and what they will be like.
My advice is trial a girl at 30mins, that minimises your monetary risk and use your instinct while you are dealing with her.