In this paper, we proposed a new agent-assisted secure payment protocol LITESET/A++, which aims at enabling the dispatched consumer-agent to choose the "best" one after negotiating with merchants to close a deal, autonomously sign contracts and make the payment on behalf of the cardholder without the possibility of disclosing any secret to any participant. This is realized by adopting the Signature-Share and Signcryption-Share schemes, and employing a Trusted Third Party (TTP). In LITESET/A++, the principle that each participant knows what is strictly necessary for his/her role is followed as in SET payment protocol while the non-repudiation property is improved.