You live in Sydney right? What is the name of the petshop you have been going to? I am in brisbane, but I can do some research on a local forum for you if you like as to whether they are a trusted shop or not.
Also, $80 for two clown fish? Unless they are generally an expensive type of clown, I wouldnt be paying $40 for a clown fish, you can generally find them in australia for $20-30 from memory, depending on shop quality, so for $40 I would hope they are some nice fish, and coming from an excellent shop!
PS - you will definately need to look into some sort of cooling for your tank, I have not been through a summer here yet with my tank (or in general as have not long moved here) but it gets rather hot, my chiller on my tank is already working quite a lot and its an open top tank and we also have the aircon going most days! Its not even summer!