Supplier Quality
For our certification we had to do quite a bit of work on this area.
We compliled a list of all suppliers we have used in the last 6 months.
Then we ranked them on quality of service to include on-time delivery, accurate delivery, customer service (after sale), etc.
Review that list prior to every order to ensure they are an approved vendor.
Audit purchase documentation internally.
Check product on arrival to ensure it meets requirements.
Document all pertinent quality data to use in evaluating the next order.
So to answer your question we evaluate all vendors.
This was a good start for us at least. Hope it helps.