The law in South Australia allows only a token maximum deposit of $100 to be paid on signing a contract to purchase. In practice this is not usually required. If the purchaser 'cools off' the initial deposit (up to $100), if paid, is forfeited to the vendor [Land and Business (Sale and Conveyancing) Act 1994 (SA) s 5].
If the purchaser does not cool off a further deposit will usually be payable once the cooling off period has expired. The total deposit is usually 10% of the purchase price. On completion of the transaction the deposit becomes part of the purchase price. The purchase price can not be paid by more than three instalment payments. The deposit may be used for either the purchase price or to pay the land agent's commission and expenses.
A deposit can be something other than cash - for example, it can be a car or a caravan, if the vendor agrees.