If you can't say yes, it's no. Just because a deal can be done, doesn't mean it should be done. Just because it may look non-negotiable, doesn't mean it is. We will do our homework before we deal. Learn as much as you can about the other side.
Instincts are no match for information or preparation.
Beware the late dealer. A deal can always be made when both parties see their own benefit in making it. Don't discuss your business where it can be overheard by others. No one is going to show you their hole card. You have to figure out what they really want.