I don't remember ever playing a stranger sets and not posting. I would always want to post the last set and pay off after each set.
If he was slow to pay and wanted to start the next set before paying you knew he empty. At this point you just take the posted last set.
However playing strangers by the game was different. If the bet was not too much I did not want to embarrass him by asking him to put it up. Sometimes if they feel insulted they won't play. To them it's just the principle of the thing.
It seemed customary to expect an air barrell back in the seventies. Many times you sensed when the air barrel was in play and boy was it difficult to nail down that last game. Sometimes just because you wanted it to end knowing there was nothing more to win, or maybe just subconsciously you wanted to keep playing. Who knows?