How would you assess a supplier's capability to collaborate and innovate, and to create value in your business?

When engaging with suppliers of strategic goods or services we can often create value through collaboration, innovation and optimisation. To gain maximum benefit we need to think about the business outcomes we are trying to achieve not simply our perceived input requirements.

Procurement generally focuses on the required product but, frequently, not enough on the inherent capabilities of the supplier. So, if we need to assess the supplier's capability to collaborate and innovate, to help us optimize existing products/services, and to achieve our desired business outcomes, how would you do this? What supplier evaluation/appraisal/audit processes do you suggest, who do you involve? Are these pre- or post-selection?

For anyone who is interested, I've set out the principles of my approach at http://www.acuityconsultants.com/news.html#how_to_select_suppliers_to_create_value

How do you select suppliers to create value?