Yep, good question. this one is a bit of a hack. Since bookings are not necessarily correlated to a mode or operator, etc, we have implemented this by detecting the informational message.
Check for stopEvents[].infos[].subtitle and see if it contains the text “Book your seat”
It’s not very elegant, but that’s how we’re doing it at transportnsw.info, and we are ensuring that this part of the text will not change.