Commissioning - what are the differences that make the difference?

I had another article published by the Guardian this week:

Is increasing public sector commissioning a good thing?
Creating dynamism or a race to the bottom? The questions we need to ask about commissioning from the private sector (You can see the article here)

The broad issue for me is how to structure commissioning so that it is a worthwhile use of public money in the short, medium and long term - taking into account all the various costs and benefits (and I don't just mean the ones that can be counted and turned into money). 

What the key ingredients for you - what are the differences that make the difference between good commissioning and bad commissioning?