I used to travel from Asia to Australia on Ansett Australia about 3-4 times a year and got sprayed every single time. Then Ansett said goodbye and I lost all my miles (having never redeemed any!) Then I switched to Cathay from Asia to Australia, and only flew a few times (cannot remember if I got sprayed).
I've done US-SYD twice over the past two years and did not get sprayed. However, most recently, I forgot that I had a banana in the outer pocket of my backpack and I placed it on the floor at the baggage reclaim. In came this little quarantine dog sniffing at my backpack and I got notated by the official (as I had ticked Nothing to Declare). I think she understood that it was a mistake. This onlooker smiled and laughed.