A method of transacting objects is provided. Each object comprises an identifier identifying an object identity. The method comprises, in a computer system, the steps of: (a) receiving transaction data from a data reader, the transaction data identifying the object identity; (b) identifying a transaction history for the object identity; (c) determining whether the object identity has been transacted in a previous transaction; and either: (i) allowing the transaction and updating the transaction history in the event that the object identity has not been previously transacted, or (ii) sending transaction history data to the data reader in the event that the object identity has been previously transacted.