Instilling an ethical behaviour in software agent environment can influence the agent to do ethical and rational actions that brings about positive impacts towards its environment. Sincerity is one of an ethical behaviour that can be considered for instilling in software agent environment, especially for encouraging the cooperation in completing tasks within an agent community. However, a mechanism to avoid imbalance in workload between software agents should be established to avoid the sincere agent from taking many tasks from its teammates until it cannot timely complete its own task. In our study, we present three evaluators in Workload Manager: (1) permission of getting favour evaluator, (2) workload calculator and (3) the progress of a worker agent's current task. These evaluators are used to evaluate the capability of an agent before taking any task from its teammate and also to determine the right time for the agent to offer the favour to its teammate. The interaction of the Workload Manager and the agent community is presented to show how it works in sincere software agent environment.