It’s not uncommon in the negotiation for you to ignore or just not realize you are making assumptions that can cause problems for you in any negotiation. Imagine yourself in this scenario: You are the sales rep. You have been working with the category buyer for weeks. The contract price, terms, and all the details have been hashed out. The contract is ready to sign. Or so you believe. Only then do you discover that the contract has to be approved by the director. And then the nibbling begins. She starts asking for additional concessions.
Never assume that the person you’re talking to is the person in charge until you ask.