A method and system for use on a quasi-public network, such as the Internet, to enable users of the network to conduct commercial transactions involving a payment of funds by one user to another user of the network. The method includes operating a computer system for sending and receiving messages from users over the network. Upon receiving a message over the network from a qualified user-seller, a message is sent over the network to the user-buyer that was identified in the message from the user-seller. The message to the user-buyer requests confirmation of a transaction identified in the message received from the user-seller. Upon receiving a confirmation over the network from the user-buyer, payment information is sent by secure channels off the network to an agent of the user-seller. The user-seller's agent may be a separate entity or the function of the user-seller's agent may be performed by the transaction enabling system. Upon receipt of an authorization code from the seller's agent, the authorization code is encrypted and sent to the user-seller over the network.