I have to a very established member, as it was an out call to cover transport etc. I paid it happily as she has a good reputation and I was a new client. I paid approx 20% of the overall fee. Then sorted out everything else when said lady arrived.
I guess it comes with trust.

But yes there are lots of scams out there. An escort, not advertising on this site, is advertising in two different locations. Gorgeous photos, but the services offered sounded too good to be true. I tried to book and deposit requested, they wanted approx 50% as a deposit. I said no and said this was a cash only business.
I guess if trust can’t be established then don’t pay the deposit. If they want to really meet you they will take cash.