Scam? Sounds like one I came across about 8 years ago.
The site had a familiar name; only 'cos they passed off as a genuine site. I recall it had the work 'belle' in it. It was lower prices than other sites, but same girls.
There was no phone number. Only online booking. And then you got into an email exchange. The address of the agency was that of a well known jewellers in Bond St!
I played along in the interest of research. Booked 'Aria' for £100 incall. The process is, that I transfer £100 to their bank and they will confirm the booking and send the girl's location.
My suspicion is, that they will make a genuine booking (through a proper agency) and you turn up and the girl will receive you, but will expect payment in the normal way. And that's when you and she will realise you've both been scammed. You for £100 and she for a non-event booking.
Watch out for these!