When and who do you pay?

There is no insurance where I live so there is no bill and no receptionist or any of that: I just hand money to the therapist and I leave. I like that: it's another reminder that this is a business relationship and that I am paying for a service. As for people who pay at the end of the month, I wonder how it works since so many people quit therapy after two or three sessions. Then what would happen if the therapist wants to get paid? Bare in mind that therapists don't necessarily know the last name of their clients which means any client can give them a random last name or no last name at all. I think therapists in my country ask for money at the end of each session as a way (among other things) to make sure they'll get paid.

In the U.S., dentists' and doctors' offices will send collections agencies after you to collect delinquent payment, and the agencies can often be quite aggressive in their tactics (calling repeatedly, hounding your family, etc). Usually a dentist's or doctor's receptionist will ask for government-issued ID before the appointment, presumably in part to verify your identity. I don't think I have ever had a therapist check my ID, but I could imagine them attempting to turn you over to collections if you owe a substantial amount.