Consulting collusive experts

Abstract In designing a contract with an agent privately informed about its cost, should a principal consult an expert who has already received a partially informative signal of the agent's cost? The expert has a prior relationship with the agent, facilitating (weak) ex ante collusion which coordinates their participation and reporting decisions with accompanying side-payments. While delegating contracting with the agent to the expert is never profitable, we show that consulting the expert is typically valuable. Changes in bargaining power within the coalition have no effect, while altruism of the expert towards the agent makes the principal worse off.