Multiple equivalent simultaneous offers (MESOs) reduce the negotiator dilemma: How a choice of first offers increases economic and relational outcomes

•Six experiments found first-offer choice (MESOs) increased offerer and joint outcomes.•First-offer choice produced greater agreement sincerity and initial recipient-value.•Agreement sincerity mediated MESOs’ effects on offerer outcomes.•Initial recipient-value mediated MESOs’ effects on joint outcomes.•Offering choice created a cooperative reputation and positive negotiation climate.