Bus More than an hour late

My sister booked in advance a city to city bus from jhb to bizana. The bus was scheduled to depart at 19:30, when we got to the bus station 45 minutes before departure time there was a very long queue and we were told the buses are finished. People started pushing their way in and some got injured. What I noticed is some people did not book tickets in advance. I would like to know from City to City how their booking process works