Listening

The underused advantage.

Why it works

Questions surface constraints, priorities and deadlines you could not have guessed. People also concede more to someone who has clearly understood them.

Summarise their position back until they agree it is accurate.
Labelling an emotion, such as this sounds frustrating, lowers the temperature.

Silence

After an offer or a question, wait. The urge to fill a pause leads people to bid against themselves, and it works in both directions.