At the weekend, I had to cast my vote in a local election arising from the death of one of the concillors. I say "had to" because voting is compulsory here.
"VOTING AT THIS ELECTION IS COMPULSORY FOR ALL ELECTORS WHOSE PLACE OF LIVING IS WITHIN ..... Every elector who fails to vote without a sufficient reason will be liable to a penalty not exceeding $110.00."
Coming from the UK (where you get a little polling card to present at a polling booth), when I attended my first election as an Australia I was quite surprised that all I had to do was tell them my name and address. No id check, no secret check of birth dates or mother's maiden name or anything else. Trust but don't verify.
The man just crosses your name off his list. That's so you don't try voting again. Except there were 11 polling places I could attend, each with their own lists. So it is quite possible to "vote early, vote often".
There is a cross check after the election between the polling place lists so they can fine people who DON'T vote. If you appear to have voted several times, you'll get a "PLEASE EXPLAIN" letter but since they don't check id, they can't really do anything about multiple votes.
Strange, but it all seems to work.