Was this in the old days of the -100 or do you mean with the recently departed Q400s? I remember when I first moved to Greece in 2005 and in winter they often would sell only 4 or 5 seats on the Paros flights, which had 34 or 35 available I believe. Others would open up on the day of travel depending on the weather and you would be called a few hours before and told to turn up and pay for your ticket. I failed to get a ticket a couple of times before I was informed that you have to go into the ticket office and pass a "Fakelaki" (a little envelope - a bribe) to the staff to ensure you were at the top of the list. This was before Olympic (the old one) sold tickets online and certainly before OLCI was a thing.