I have a friend who works as a salesperson at a 4S dealership.

He said that the time when customers haggle the most is often when they want to buy the most.
Those who are not really interested, after asking for the price, just leave and don't bother to haggle.
So their first training lesson is:
The more a customer insults you as being shady, the more you should serve tea and pour water.
After they get tired of insulting you and see your good attitude, there's a high chance they'll sign the deal.
He said whether a car sells well or not doesn't depend on the car,
It depends on whether the salesperson can keep smiling when being insulted.