I have put a RB on AW recently and received a reply.
I then received a very short message saying that she charges half as a deposit
https://www.adultwork.com/3145099 or https://www.adultwork.com/abbietuffers60
This kind of thing happens fairly often (I do most of my meetings as RBs and one or two replies always mention a deposit). Most of them are a bit like this one, in that they are usually from people I have no wish to see (in this case, it's bareback and a brand new profile which would be red flags for me).
Sometimes you do get this request from people who have better profiles and feedback. In every single case, these people have dropped the request for a deposit if I write a short, polite message back saying that I will never pay a deposit, that this is a 'cash on arrival' hobby, and that if you can't agree on that then there is no point in messaging any further. Just be firm about it but not rude.
The same goes even if the deposit is supposed to be 'for travel expenses' (which is another line I quite often see).