Erm, well I am to babysit this 5 year old, the wonderful problem is..he is basically a spoiled brat. Usually he is fine, behaves well and eats well (good stuff), but sometimes he just starts screaming his guts out, typically because something is NOT going his way. Any ideas on how I can deal with that? I know it is a weird topic, but may be someone has experience. I can't possibly keep on spanking him/yelling back, since it will not solve anything.
Any advice will be appreciated.

I babysat older kids, 12-13 years old, but I figure you can give it a try. If there's something that he wants to do, watch tv, play outside, anything that is considered a want not a need, tell him that he can't do it tomorrow unless he can be good for that day, which includes no screaming. You have to emphasize that it includes no screaming or anything else that is considered "bad behavior".

A kid I had to babysit was a bit spoiled herself, and she wouldn't take her medicine or wake up when she needed too. She'd just bitch, moan, and complain when I tried to get her to do it and goes into this "It's my life I can fuck up if I want" rant. I've recently took a mental note of what she likes to do, that doesn't effect my wallet, and asked her if she wanted to do it tomorrow. When she said yes, I told her that she could only do it if she was good, which for her was getting up on time and taking her medicine. It works mostly because I really don't want to do it, but she really wants to. When she goes into pouting mode, I ignore her.

If the kid screams because he doesn't get what he wants, just go into a separate room, shut the door, put on some headphones, and ignore him. Unless he's violent, it's best to let him scream himself out. Eventually, he'll notice that it's not helping him get his way and he just ends up with a sore throat in the end. He'll notice that it's not worth it and give in to you. Even though the girl I take care of has parents who don't really make her do what's best for her, she eventually realized that when I'm taking care of her, she has to do what I say and what her parents usually do. Unless the kid really hate you, he'll give in. I know this because my friend who she hates used the same method as me, and she threw a fit and refused to give in. They fight less when they like you.

You also have to develop a good relationship with the child for the reason mentioned above. Once they decide they don't like you, they'll never like you. When they never like you, they'll never give in and only push back harder and resist more. First, make sure they look up to you and like you, then find out what the kid likes, then tell them that you'll do it tomorrow if they are good. Three easy steps.