Marjorie's Law of Greek Public Transportation:
If you ask a helpful information desk employee about the bus and they tell you, "Right across the street, every 20 minutes," that is a sure sign that there is a public transportation strike in progress.
If you ask a helpful hostel desk employee about the bus and they tell you, "There's no buses or metro today, and I think the airport's closed so your flight will probably be canceled," that is a sure sign that all public transportation systems are running perfectly.
n=3.
Happily, the latter example happened when it was time for us to fly home, so we got to the airport with no problems.
One picture before I head to bed: