I wouldn't say its greed. I would say its desperation. WGs do not put their prices up as they are getting enough business to satisfy them. The whole notion is a contradiction in logic.
Before they did thier ultimate Gerald Ratner moment, girls like Tori Taylor, Scarlett Sage and Daisy May were the lowest priced girls to book in the region and for a very long time actually undercut the agencies £110/hr price increases as they stuck on £100 an hour. The reason why is clear, they were fit, and getting bookings by the shed load so didn't need to change anything.
You will notice the girls putting their prices up beforehand they suddenly take a large interest in posting on places like Twitter, and bang on about getting a cat and being obsessed with his every move.
I am going to paraphrase what JimmyRedCab used to say all the time. Popular girls do not post on twitter, it is only the dusty phone brigade desperate for bookings.
I am going to add my own to that. Popular girls do not own cats and post about them non-stop. As they would have other things to occupy their time with - i.e bookings, or spending money earned from the bookings. There is a reason why the phrase crazy cat lady came about and it's not because they are busy.
When the above girls claim of price increases as they are "so busy" it is a lie. It is a price increase because nobody is booking them. If people were booking them they wouldn't have time for silly waste of time places like twitter.
Don't book them. They will put their prices back down when they realise it doesn't work. If a WG is not getting enough bookings, she shouldn't put her prices up to compensate. She should put her prices down. Or offer discounts. No other industry when there is not enough customers does the business put the prices up to compensate.