@Sean95
I've just checked this out using my partner's account for my listing. Here's what I discovered:
After I chose "Reserve", the "Rules" page appeared. All the preset rules that I've chosen (no pets, no parties, etc) are listed. The box must be expanded through a "Read More" drop down to see any additional rules that I've added. In my case, I've included a "no 3rd party booking" rule and a couple of other things.
The booker must then click "Agree and Continue".
They are then presented with the prebooking message, in which I've asked for arrival time (after 3pm) name of second guest (if any) and a **Note: 3rd party bookings violate Airbnb's terms of service. Please abandon this booking now if you will not be staying here personally.
You can tell that I have a problem with 3rd party bookings 🙂
Anyhow, the booking is not confirmed at this stage, so I guess it is still a PREbooking message that guests are presented with before they confirm the reservation. A "Continue" button must be clicked before the order is processed.
I've only just added the 3rd party biz into the prebook message, so I'm hoping that I see a drop in people doing this going forward. Obviously no one expands the "read more rules" part (which seemed to make no difference - or at least didn't discourage ALL third party stuff), so I though I'd try this.