How we change what others think, feel, believe and do
Appear angry with them over some detail.
Take slight about some small thing they say. Turn a neutral comment they make into a personal attack on you. Be emotionally sensitive about odd comments. 'Misunderstand' something.
Berate them about not knowing 'important' details.
You can also get cross about something completely different, such as someone else or some other situation.
Then, when they are trying to calm you down, ask then for some concession.
What do you mean 'cheap'? Do you think I'm a cheap person?
Getting angry about anything or any one is yet another emotional distraction that says ‘Forget about the real subject in hand, just focus on calming me down. Giving in or making some concession would be a great help, by the way.’
Faking emotions is normally quite difficult, but anger is one of the easiest. Even if unsure, the seller is unlikely to challenge this, as to question the motives of an angry person is to risk an even greater explosion.
Some people use anger as a part of their normal persona, getting cross about anything that gets in their way and using anger as a shield and an excuse for aggression.