A quick browse of the reviews section shows that it's a fallacy to correlate higher prices with better service, and lower prices with bad service.
We're talking about prostitutes. Not expensive cuts of meat, or truffles, or a top-of-the-line cars (tangible luxury commodities). Sure, it's logical that a pretty girl can get away with charging more, but that doesn't mean her head will be in the right place and she'll have a good attitude.
SexyNicole19 and Katalina are just two examples of sub-£100ph girls that deliver the goods. The former of those two is now in central London and still charging £80ph and she's probably prettier, younger and has a better attitude than most of the overpriced crap on agency websites. Hopefully Jimmy never visits her, or she'll shoot up to £100+ ph.