Has an AFL game ever ended 27-18?
Exactly once. On May 24, 1900, Carlton beat St Kilda 27-18, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 27-18 in league history.
That makes 27-18 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 28-18 has happened never and 27-19 has happened never.