Based on what I've seen it looks as if the girls may be allowed to set their own prices. Below is something they posted about pricing. It's not a bad approach but they do need to explain things better about how the prices work
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The agency is currently available five days a week from Monday to Friday, with appointments available all day between 11 am and 8 pm, with last appointments at 7:30 pm. It’s an independent service that allows escorts to choose their working days/hours, so it’s advisable to get in touch by phone to check for availability, once you’ve picked someone you particularly like. Standard rates start at £80 for 30 minutes, up to £280 for two hours ( services).