The generally received wisdom is: never, under any circumstances pay a deposit.
There's simply no good reason for it for a UK booking, and it is an abnormal request. Overwhelmingly, UK SPs do not require one, except and unless you are proposing flying abroad with them for several days: and even then, not always.
As for this particular girl's claim that it's for the 'extra admin' that an incall entails, that's just laughable. If a SP is citing that she has previously suffered no-shows - a small amount is to be expected and is accounted for by her handsome first hour's fee. If she is persistently encountering no-show problems, it's almost certainly a reflection of her own lack of administrative and organisational skills.
In this case, it may be that as an Australian who only registered for AW in late June, she is not sufficiently familiar with market norms; or else simply doesn't know what she's doing. Much of her AW feedback to date is from one ID, and is therefore suspect.
