It is not the manager’s job to do whatever the customer wants. It is the job of the manager to do what will help the company be profitable. Screaming at the manager will not cause him to do whatever you want. If your demand is unreasonable and you are being an asshole he does not have to do anything for you. Most managers do want to help the customer and do what is right but if you attack him as soon as to walk in the door demanding stuff do not be surprised when he resists. Many managers follow the philosophy of assuming the customer is lying till you can prove they are not and screaming does not help prove you are not lying. Managers are people too but if they have been a manager for more than a day, then they will have already had many people yell at them demanded stuff so do not surprised when the manager does not just bend over and give you everything you want.