This paper proposes a new distributed reputation management scheme to support agent-based applications. The scheme uses a transaction feedback system and five metrics to real-time evaluate the reputation of Trusted Third Party (TTP) hosts that are selected and employed to support an agent in performing its transactional tasks. The scheme exhibits two interesting features not seen in previous works: firstly, it offers better efficiency and robustness, and secondly, it credits/penalizes a TTP-host according to its transactional response, the transaction value and the reputation of the source of feedback. In addition to facilitating TTP-host selection based upon its reputation, this mechanism of credit and penalisation is expected to deter dishonesty or misbehaviour by the entities involved.