“…110 Over the centuries the principle evolved providing various measures for a just price, 111 to modern rules now referring to 'unfair advantage' in the parties rights and duties, also extending the scope of the principle to a broader range of contracts and to protecting both parties from paying too much. 112 In regulating unfair advantage, some countries have fixed limits. In Austria, laesio enormis allows a contracting party to rescind the contract who received less than half of the fair value; 113 fair value being determined by reference to the average market price; 114 unless circumstances exist that void the rule such as when the party knew the true value or accepted the disproportionate performance out of special preference.…”