Two things
1. So when an SP takes an instant dislike to UKP even if they have had glowing reports, what do you suppose is going through their minds, is it simply a personal preference. I am thinking of a well known BBW sp who works out of Tipton and despite many good reviews she remains adamant to refusing their business. I am sure your answer is different strokes for different folks but it seems a little anti-business 
2. It’s often been said that a negative review can be a benefit to SP as well allowing her to review her modus operandi and improve her game if she wishes. There are several SPs who start out with a bunch of negatives then suddenly go positive and never look back. I am sure your answer will be the same as above.
In civvie world if I leave a review on google maps or tripadviser even if the review is positive, if you say you don’t like the wallpaper then you usually get a terse response. It’s why the only acceptable review is a 110% positive. Same goes for Adultwork feedback and why it is dismissed so strongly on here.
Musings over but this stuff regularly raises its head
Just curious about how you see it 
It's an interesting one I as I said above i don't think a lot of SPs understand how forums work or how to make them work for them, there are many influences clouding someone's judgement of a site like this.
There is the influence of other SPs on sites like saafe, or other girls they meet in person.
Unnecessary information being put into a review, too revealing or personal.
One thing I belive gives girls a negative view of here are the picture collectors, there is a thread on the London board atm where guys are reminiscing and sharing dozens of pictures of SPs they have punted, most of those girls are retired and no longer working, these guys have kept these pics for years, girls just don't need that if they retire.
I can only speculate as to why girls would refuse someone a booking on the basis of them being a member here
Possibly if they were a known BB punter or their online presence was very misogynistic like KT for example and they made their membership obvious, aggressive language in reviews can also be scary for girls, I've read things like, ....so I pushed her face down and fucked her as hard as I could, thats not something most girls want so fear may be a factor.
I actually think like you its very possible for an SP to learn from reviews and improve the service they offer, I learn all the time from my reviews and from others.
I do wish girls would learn to work with forums more as I think it would be much less stressful if they did and punters interacting on forums with SPs also learn about this industry from a different perspective.