QoS abuse. Malicious service providers may strategically alter their behaviour in QoS offering in order to obtain profit. For example, malicious service providers may use successful service transactions with small amounts to build its reputation, obtain service consumers’ trust and then defraud them of their money with fraudulent service transactions with large amounts. Genuine service providers may also strategically alter their behaviour under a certain circumstance, e.g. given an order of a service transaction with an unusually large amount, a genuine service provider might make the transition into being a malicious service provider and then provide a fraudulent service transaction. Take the composite service presented in Section 2.6.1 for instance, in order to boost its reputation, a malicious land carriage company can manipulate or fake several clients to get good ratings over poor or fake service transactions. These manipulative ratings will jeopardise the accuracy of service consumers’ evaluation of their trust over the land carriage company. If such service providers are selected to provide the component services, the actual success rate of the composite service will be lower than the service consumers estimate it would be. In addition, a malicious land carriage company can perform some service transactions with low transaction amounts to boost its reputation. By doing so, it can take advantage of its high reputation to attract potential big clients and defraud them of their money with fraudulent services with large amount. This may cause violations of the service consumer’s requirements for the composite service because 1) the land carriage service has to be rearranged; and 2) the shipping service may have to be rearranged too. To resist the threat of malicious reputation manipulation, service consumers’ trust over service providers should be evaluated based on service providers’ long-term reputations which are evaluated based on service providers’ long-term performance. Long-term reputations can smooth out short-term fluctuations and highlight long-term trend of service providers’ reputation. Another benefit of basing service consumers’ trust over service providers’ long-term reputation is that it encourages service providers’ trustworthy and consistent behaviour at present. To resist the threat of QoS abuse, when evaluating service consumers’ trust over individual service transactions, the QoS of the past successful service transactions that the service pr...
