Has an AFL game ever ended 189-18?
Exactly once. On July 26, 1919, Sydney beat St Kilda 189-18, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 189-18 in league history.
That makes 189-18 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 190-18 has happened never and 189-19 has happened never.