This is almost the reflex of the last post the difference being that being the one calling the shots you will usually be trying to construct a framework of everything you want. If your supplier is any good (and you want them to be) then they wll challenge you out of your mindset and the two of you will get to a better place as a result. One of the challenges when working with a supplier is that you do want them to jump when you say jump. But you don't want them to tell you only what you want to here. Encouraging them to ask frank and challenging questions is also an art. You could always ask them if there's a question which they'd like to know the answer to but which they're too embarrassed to ask. We need questions which don't allow the supplier to get away with whatever but which raise the bar - so they perform better.

Criticism ought to be constructive - for their benefit and not just because you didn't get what you were expecting. But I have had difficulty on that front where suppliers have taken great umbrage when I gently pointed out that they could have done better. Perhaps I should have lost my temper and shouted and that would have been all right. But win win means that both need to come out of a conflict situation intact and hopefully improved.