In multiagent interactions, such as e-commerce and file sharing, being able to accurately assess the trustworthiness of others is important for agents to protect themselves from losing utility. Focusing on rational agents in e-commerce, we prove that an agent's discount factor (time preference of utility) is a direct measure of the agent's trustworthiness for a set of reasonably general assumptions and definitions. We propose a general list of desiderata for trust systems and discuss how discount factors as trustworthiness meet these desiderata. We discuss how discount factors are a robust measure when entering commitments that exhibit moral hazards. Using an online market as a motivating example, we derive some analytical methods both for measuring discount factors and for aggregating the measurements.

While diffusion of innovation topics in economics and majority games in game theory have been widely studied, the impact of economy-of-scale effects in aggregated decision making has received little attention. In this paper, we present a basic model, the Game of Scale, to study the effects of economy-of-scale in decision making among a large pool of self-interested agents. We solve the model's static equilibria and present two dynamic decision models, one myopic and one trend-following. Most of the parameter space converges quickly; however, the behaviors exhibited near critical input values show drastic changes. We demonstrate how trend-following can improve global outcomes over myopic decision making. Finally, we describe how the game can be externally controlled.