What the heck?
On most buses there'd be 1 driver and 1 ticket collector, at least by the 1990s. There might be 2 collectors on long articulated buses, one near the front and one near the back.
The last vestiges of that system were phased out with the drachma/euro conversion around 2000, when everything had to be changed over anyway. Nowadays most Greek cities use a proof-of-payment system, where you have to buy and/or validate a ticket yourself from self-service machines. Then roving inspectors get on buses randomly and fine people who can't produce a current ticket.
The old system has been gone long enough that there are nostalgia articles like, "Do you remember the days when buses had an 'eispraktoras'?". The last two photos here show a ticket collector station at the rear door, which would have a cash drawer under the counter for making change: https://www.enimerotiko.gr/ellada/thymasai-tote-poy-ta-leofo...