A great negotiator understands what both parties to a deal want. He investigates, listens, probes, and aids you as you determine what outcomes you want from a deal and how best to achieve them. But he also listens to the other side and figures out what they want, then crafts the deal so that the other side can see the benefit and come to the table. Finally, he keeps constantly vigilant to the risks the deal can pose and helps you minimize those risks. As a negotiator I have crafted and/or counseled in the crafting and completion of deals in multiple industries.
Frequently in my professional career, when a deal is done, the party on the other side has hired me to represent them in the next deal they do.