I’ll let you in on a secret. There are actually three kinds of “Yes”: Counterfeit, Confirmation, and Commitment.
A counterfeit “yes” is one in which your counterpart plans on saying “no” but either feels “yes” is an easier escape route or just wants to disingenuously keep the conversation going to obtain more information or some other kind of edge.
A confirmation “yes” is generally innocent, a reflexive response to a black-or-white question; it’s sometimes used to lay a trap but mostly it’s just simple affirmation with no promise of action.
And a commitment “yes” is the real deal; it’s a true agreement that leads to action, a “yes” at the table that ends with a signature on the contract. The commitment “yes” is what you want, but the three types sound almost the same so you have to learn how to recognize which one is being used.
Voss, Chris; Raz, Tahl. Never Split the Difference: Negotiating As If Your Life Depended On It