It's subjective. I do, however, use the "less than £100 ph" line as a marker for skepticism when viewing a profile. A positive review on UKP will allay any fears I have though.
In my punting area the 120/150 an hour seems to be average with WGs charging above that needing to justify it through service and/or looks.
Essentially it boils down to whether you feel the service was worth the rate you paid. Which in turn influences whether you will return to said WG.
I agree with the thinking behind this.
Oop here in t'north, I wouldn't normally consider any "mature" WG charging less than £80 p.h. and Reviews have to be really enthusiastic to tempt me to pay over £120.