Deposits are nothing new but should always be avoided. Its always a scam in my opinion and they will conveniently disappear off the site or start ignoring your calls and texts once they have their hands on your hard earneds. Any honest and respectable escort will learn to take the rough with the smooth and take the odd hit for no shows, whereas those asking for deposits tend to be either dreamers, fantasists, arrogant and thinking they're God's gift or thieves.
The dodgiest and normally most insistent that deposits are needed will come up with some weird and wonderful reasons why deposits are necessary; to prove you are genuine, to compensate in case you are not genuine and stand her up, to 'secure' a booking as they are so busy and so special that they're doing you such a big favour by offering to see you, but ultimately its all bullshit to take your money and run. Don't be fooled and don't do it as it sets a precedent and they will all start trying it on if they can find gullible guys who offer up their pennies freely.