Renting a car in another country, is it the same as in USA?

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I'm going to be taking a trip to Australia next month and so far I've got everything confirmed except for my car hire reservation. I know how hotels and everything work, but is there any difference between renting a car in the USA, which I do frequently, and renting one in Australia, which I've never done before? Can I just show up at the airport and get one there, or should I go to one of those sites ( http://www.121carhireaustralia.com/ ) and set up the rental ahead of time? In Australia, will you get a worse price if you rent it on the spot compared to if you schedule it ahead of time? I know that's how it works here in the states but I don't know if other countries are the same way. I don't mind scheduling it ahead of time online, but I like to keep my options open until the last possible minute just in case, so let me know if I can do it that way. Thanks!