Service level agreements to measure the results. Guidance in how to govern the relationship. Dealing with the transition. The pricing structure. Each of these items has its own idiosyncrasies.
Intermediaries ensure buyers lead the discussion.
Even more important, they work to align the buyer's interests with the vendors' - the clearest recipe for outsourcing success. Paying By Problem Resolution Customers often push to pay their suppliers by problem resolution. While this sounds like an elegant solution, it is really a short-sighted approach. Buyers paying only to fix problems are giving the supplier no economic incentive to correct the systemic, underlying causes of those problems. It's like a physician treating the symptoms but ignoring the disease.