[20] The first appellant, Heritage Corporation (Aust) Pty Ltd, is a company carrying on the business, inter alia, of trading in goods and other commodities. The other appellants are directors of that company. The first appellant is a member of a number of trade exchanges, and in particular Contrabart Trade Exchange operated by Contrabart Trade Exchange Pty Ltd ("Contrabart'). That company facilitates bartering or counter-trading using as the medium of exchange for trading goods and services credit units called in this instance "trade dollars". Members of the exchange who transact business express the value of their transaction in trade dollars. As a result of the transaction, notice of which is given by a document called a transaction slip to Contrabart, a number of trade dollars will be debited to the account of the buyer and credited to the account of the seller. Members of the trade exchange pay Contrabart a small monthly fee and are obliged to pay a commission of 10% on the acquisition of property or services. The monthly fee is payable partly in trade dollars and partly in legal tender. The commission is payable wholly in legal tender.