Most people seem to agree that you shouldn't buy ferry tickets until once in Greece.
Can you show up the day of and book tickets? (going in November so I don't think they'll be a lot of passengers competing for seats).
How long before the ferry leaves should you be at the port to buy tickets and get aboard?
Do the rules changes on overnight ferries versus day ferries? (because more people book beds/births for overnights)
Could I buy a ticket for Patra to Corfu, etc at Piraeus?