I get the impression that most escorts form an opinion of their 'worth' and pitch their prices accordingly; also relative to the number of clients they can tolerate in a business day.
So beautiful ladies like Sophie night, Natasha, Carmen and Salina ask a little more but use the higher fees to attract the right number of clients and presumably of better quality.
If business drops off they can reduce prices, if there are just too many phone calls they elevate fees; Salina and Natasha now charge 150 for 30 minutes instead of 125. Summer now advertises the 180 per hour VIP service, with presumably no 30 min rate.
Shelby puts it very succinctly; "So determine what you want to pay and find a provider in your price range". Blunt but accurate. Bargaining with providers just pisses them off mightily.
