While it may sound easy, there are many things which you need to have a rather good knowledge of to complete this effectively. First, you need to have knowledge of construction. This may seem obvious, but many places have been left worse off than they were originally because someone bit off more than they could chew. You need to be able to identify supporting walls so you can maintain the structural integrity of a building versus a wall which is simply cosmetic.
You also need to be able to realize when something is simply a cosmetic issue or if it is a sign of something more dangerous. Mold for instance may be cosmetic, but could be an indicator of a leaky pipe or roof. If you see something which looks like a crack, it could be the paint or it could be bad construction. These are things you need to be able to tell rather quickly before sinking more money into a house's repair than you'll get back in the return.
On top of these things, you would also need a good electrician and plumber whom you could work with and trust. These are two points in house flipping which cannot be skimped on. Codes change constantly and you as the owner will be held liable if something is wrong with either. While it is true that you can go after whoever wronged you, at the end of the day it will be your reputation which is tarnished.
Flipping larger buildings, while obviously on a much larger and more expensive scale, is really the same idea. It has been shown to have the possibility to be very lucrative and if done correctly, can continue to turn you a profit many years down the road.
If you are interesting in beginning to flip houses or buildings, do your research first. You are going to want to be sure that it is something you think you can handle and maybe reach out to others who flip already to get an insider look. It is another way to vary your abilities, and will make you seem extremely well rounded if you can show you are successful in doing this as well.