Inspired from the ideas such as "algorithm portfolio", "mixture of experts", and "genetic algorithm", this paper presents two novel negotiation strategies, which combine multiple negotiation experts to decide what to bid and what to accept during the negotiation. In the first approach namely incremental portfolio, a bid is constructed by asking each negotiation agent's opinion in the portfolio and picking one of the suggestions stochastically considering the expertise levels of the agents. In the second approach namely crossover strategy, each expert agent makes a bid suggestion and a majority voting is used on each issue value to decide the bid content. The proposed approaches have been evaluated empirically and our experimental results showed that the crossover strategy outperformed the top five finalists of the ANAC 2016 Negotiation Competition in terms of the obtained average individual utility.

Utilizing witness information to supplement direct evidence is commonly used to build assessments of the trustworthiness of agents. The process of acquiring this kind of evidence is, however, typically assumed to be cost-free. In practice, agents are budget-limited, and investments in acquiring witness (or reputation) information will affect the budget that can be used for direct interaction. At the same time, acquiring such witness information can help in making better trust decisions. We explore this trade-off, formalising it as a budget-limited multi-armed bandit problem, and evaluate the effectiveness of algorithms to guide this decision process.

Online communities use trust and reputation systems to assist their users in evaluating other parties. Due to the preponderance of these systems, malicious entities have a strong incentive to attempt to influence them, and strategies employed are increasingly sophisticated. Current practice is to evaluate trust and reputation systems against known attacks, and hence are heavily reliant on expert analysts. We present a novel method for automatically identifying vulnerabilities in such systems by formulating the problem as a derivative-free optimisation problem and applying efficient sampling methods. We illustrate the application of this method for attacks that involve the injection of false evidence, and identify vulnerabilities in existing trust models. In this way, we provide reliable and objective means to assess how robust trust and reputation systems are to different kinds of attacks.

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