Described is an optimistic fair payment protocol in electronic commerce that provides fair payment while resisting an unconscious double spending attack and other attacks. A buyer receives encrypted e-goods from a merchant, and sends payment to the merchant. If decryption information is not received in exchange for the payment, or the decryption information does not render the e-goods useable, the buyer launches a dispute with a third party dispute resolution service. If the decryption information is received and renders the e-goods useable, the buyer determines whether the e-goods are valid, according to a corresponding description. If not valid, the buyer launches a dispute and provides the e-goods and the description. The third party uses the description to evaluate the validity of the goods to determine whether to refund the payment to the buyer or release it to the merchant.