My top tips..
1- Knowledge is power- The more you know about the price of your cloth/rivets/laundry processes/raw material market value/cost of a beer in Turkey the better. Arm yourself with numbers.
2- Be nice- This should be easy, but in business is often mistaken for weakness or naivety, I am not a doormat! I would rather build a relationship with my suppliers and work together in a fair, positive and respectful environment. I am confirming an order not waging war!.. However.. If I feel I am being taken advantage of... the fangs come out, and my teeth are sharper than yours!
3- Keep quiet- Silence is a powerful tool, let your suppliers do all the talking. I promise, you will get to where you need to be much quicker than rambling on and losing focus of your target!
4- Wear a Blazer- What can I say, the shoulder pads give me special powers!!