Commercial Bank of Australia Ltd v Amadio, is a seminal case in Australian contract law and equity, in which the High Court held that unconscionable dealing due to a lack of knowledge or education and the consequent imbalance in bargaining power could lead to a transaction being set aside. The case is a formative case for the defence of unconscionability, a precursor to statutory unconscionability. Background Facts Giovani and Cesira Amadio, whose son, Vincenzo, carried on business as a builder, guaranteed their son's indebtedness to the Commercial Bank of Australia. To this end, they executed certain documents the effect of which was to provide the bank with a mortgage over a building which they owned. When the son's business failed, the bank sought to enforce the guarantee. In their defence, the Amadios asserted that the guarantee was unenforceable because it was unconscionable. They were held to be at a "special disadvantage" as an equitable doctrine in Equity (law). With unconscionable conduct having no definition at a legislative level (other than conduct lacking in goodfaith) it is largely up to the presiding judicial member to determine as to whether compliance is efficient on a statutory basis. Supreme Court The Amadios commenced proceedings in the Supreme Court of South Australia seeking to set aside the mortgage and guarantee. In relation to the claim that there was an unconscionable bargain and the claim that the bargain was procured by undue influence, Wells J delivered an ex tempore judgment in favour of the bank, holding that there was nothing to suggest to the bank officers that the Amadios did not understand the guarantee or the financial predicament of the son's company. The son had spoken to his parents in Italian, in the presence of the bank officers, giving the bank officers the impression that the Amadios understood the guarantee and financial indebtedness of his company. In fact, the son had withheld the key information from his parents to try to maintain the appearance of success. Wells J held that the transaction was "an ordinary one, struck in the usual and regular course of commerce" and that the bank "was under no legal or moral duty to acquaint themselves with the underlying facts". His Honour held that any hardship, or inequality of bargaining power, was unknown to the bank and the transaction was not unconscionable. Wells J concluded with these remarks: "where one or other