How does a party ensure that opposing party is serious about mediation?
You can never really be sure that the other side is taking the mediation as seriously as you are, but you can increase the likelihood that they take it seriously by doing several things.
First, be prepared and prepare the other side. If you don’t prepare them for what is to come, they may just be getting ready for the fishing expedition you hope to avoid. Get the information and analysis to the other side in advance (if you want that information to be considered by them) and consider submitting your initial proposal or conceptual goals to them in advance as well.
Next, time your mediation so that they should take it seriously, and discuss who will attend in advance. Finally, select a mediator that will work hard to try to help you avoid wasting time. Even if the case does not settle, good mediators can help both sides make real progress.