Some agencies do charge a 1 or 2 of their girls book-on fees because ----- they are the girls that give the "office" a schedule of when they want to work, they call in and book on, and then the phone lady books them a client -- when the phone lady calls the girl to let them know they have a client, the girl does not answer her phone, she is "sick", drunk, whatever ... and blows the call off.
If a girl is notorious for this kind of behavior, the madame will charge her a book-on fee - it is like a small punishment --- heh, you want to work for me and pull this shit? I will charge you $10 every time you book on, to give you some insentive to show up for work. This book on fee does not last for long .... most girls either go to another agency or they start behaving and show up for their shifts.