As a rule of thumb, you should avoid unless they let you contact them by another channel.
They should let you call or email them if they are true about the escort service. Even more, if they let you contact them by another channel but then they ask you to discuss the meet over the webcam you should still avoid.
Think about it. What is an escort booking over the webcam requirement? In the best-case scenario, it is a hidden fee, in the worst-case scenario, it is a scam and the girls will try to get you on cam as long as possible without any intention of escorting. In either case, it is a dishonest behavior.
Girls will try to justify it by saying that they need to know you first. That's is a lie. Are they going to have sex with you without asking for money? They are not girlfriends, they don't need to know you first.
So, unless you genuinely want to enjoy a webcam session and discussing a meet wasn't your first intention, avoid.