Just a couple of extra points I thought worth mentioning - there are two types of warranties that can be applied to a purchase - manufacturer warranty, and retailer warranty.
Manufacturer warranties are the ones that are provided and honoured by the maker or brand - eg Sony provides the manufacturer warranty for Playstations. The reason why these generally won't be honoured if the purchase is not through an authorised retailer, is because the purchase and therefore whether a warranty claim is even valid can't be verified - as a more clear example if you buy a brand new PS5 off the back of a truck (AKA stolen) and it is faulty, why should Sony fix it for free? If it comes from an authorised retailer, the supply chain can be verified and it's clear that everyone who was supposed to made their money, and that it was a purchase that Aus consumer law actually applies to. (On this note, manufacturer warranties can still be dealt with by the retailer, if you ever take an item back to a shop and they say they can't do anything, that you have to contact the manufacturer, while you can do that if you want to, they are shirking their legal obligations).
Retailer warranties are 100% offered and honoured by the business that sells you an item - often they are selling the warranty, rather than offering it for free, though (eg The Good Guys offering a 5 year warranty on a tv for an extra $100).
The most important thing to remember about either of these types of warranties is that they are voluntary - no business or manufacturer has to offer them (though they are technically legally obliged to honour them if they do), but consumer guarantees, on the other hand, are mandatory, and most warranties don't offer much (if anything at all) above and beyond what consumer guarantees provide by default. Consumer guarantees apply to purchases from anyone who is carrying on a business in Australia, whether they are a registered business or not, or even located here, but it is a lot easier to enforce them (if it is necessary) if they are a registered business located here, and practically impossible if they are not located here. (i.e. as already mentioned, the consumer guarantees may as well be non-existant for a business located overseas who doesn't voluntarily honour them).
The moral of the story is the same, regardless, though - buy expensive items, where warranties / guarantees are an important factor, from reputable Aussie businesses who can't disappear overnight.
