It is inevitable that parties enter negotiation, whether in mediation or otherwise, making assumptions about the other sides’ negotiating position, their needs and drivers.
Unfortunately making assumptions weakens a negotiation position – the more assumptions that are made, the riskier the position.
In mediation the Mediator can be used to turn assumption into fact, and so move your negotiating position to a sounder, factual, base.
Before making an offer or counter-offer why not ask the Mediator to check out your assumptions? After all, his/her role is to help your client (and the other side) get the best deal, so make use of their unique position to turn your assumptions into facts.