To be fair, I think its the WG's who are mostly at risk.
Why bother mugging a single punter, when you can mug the WG after she's finished her shift?? She, potentially, could have several times the amount a single punter would have
Unfortunately, I've heard of this exact thing happening in Nottingham previously......... and worse.
At one time, a guy would meet the WG (at her or the agencies premises) have his session, leave, then mug the girl shortly afterwards, as she left. He got his money back, plus whatever else the WG would have on them (cash, phone etc etc)
There are all sorts of risks for everybody involved in this pastime of ours - we should all look out for each other