Towards Efficient Trust Aware E-Marketplace Frameworks Malamati Louta Harokopio University of Athens, Department of Informatics and Telematics, Greece Angelos Michalas Technological Educational Institute of Western Macedonia, Department of Informatics and Computer Technology, Kastoria, Greece INTRODUCTION In the liberalised and deregulated e-marketplace some key factors for service providers’ success are the following. First, the efficiency with which services will be developed. Second, the quality level, in relation with the corresponding cost, of new services. Third, service providers’ reliability with respect to service provisioning. Fourth, the efficiency with which the services will be operated (controlled, maintained, administered, etc.). The aim of this paper is, in accordance with efficient service operation objectives, to propose enhancements to the sophistication of the negotiation functionality that can be offered by e-commerce systems in open competitive communications environments. In the highly competitive and dynamic e-marketplaces, Service/Product Requestors (SPRs) should be provided with mechanisms that enable them to find and associate with the most appropriate Service/Product Providers (SPPs), i.e., those offering the desirable quality of service / product at a certain time period, in a cost efficient manner. Such mechanisms may entail a wide variety of negotiation mechanisms, including auctions, bilateral (1 to 1) and/or multilateral (M to N) negotiation models and strategies, as well as posted offer schemes (i.e., a nonnegotiable, take-it-or-leave-it offer) in order to establish the ‘best’ possible contract terms and conditions with respect to service / product access and provision. Efficient e-marketplace operation requires for a cooperation of high degree among the various entities (SPRs and SPPs). However, seeking for the maximization of their welfare, while achieving their own goals and aims, entities may misbehave (intentionally-acting selfishly or unintentionally-due to faults), thus, leading to a significant deterioration of system’s performance. Therefore, trust mechanisms should be exploited in order to build the necessary trust relationships among the e-marketplace entities, enabling them to automatically adapt their strategies to different levels of cooperation and trust. In related research literature, reputation mechanisms are employed to provide a “soft” security layer, sustaining rational cooperation and serving as an incentive for good behaviour, as good players are rewarded by the society, whereas bad players are penalized by spreading in the market their bad reputation. In general, reputation mechanisms establish trust by exploiting learning from experience concepts in order to obtain a reliability value of system participants in the form of rating based on other entities’ view/opinion. Reputation related information may be disseminated to a large number of system