quicko: undersold ...

I find this truly bamboozling (and quite possibly my best answer to "what's the strangest Australian custom?" to date):  the number of times I've been sold less than what I wanted to buy.  Generally this involves hot chocolate and an "American small" (AKA "large" here) that I wish to purchase ... when, suddenly, somehow, I discover that I've been persuaded to buy an "American microscopic" (AKA "regular" here).  Here I was, prepared to pay, set to spend, ready to retail and, presto!  More cash in my wallet and less chocolate in my tummy.  As I said, truly bamboozling.