• Knowledgeable (has to know the law)
• Experienced at mediating (too many “wannabes”)
• Litigation savvy (knows the true costs and challenges of litigation)
• Empathetic (a good, sympathetic listener is a must)
• Diligent (a mediator has to know the issues and subtleties)
• Firm (a mediator has to know when to read the “riot act”)
• Stamina (mediation is often a marathon)
• Adaptable (a mediator wears many hats)

If the other side suggests a mediator you’ve never heard of, ask around. What do your colleagues think and what is the mediator’s reputation like? To be honest, I’m never too quick to agree to a mediator suggested by opposing counsel if I don’t really know their style and reputation. Opposing counsel may have a comfort level with the mediator or know something you don’t that could work against your client. 

By keeping the above characteristics in mind and doing your homework, you and your client will likely have a better chance of satisfactorily settling the dispute.