Professional builders and skilled professionals, such as carpenters and plumbers, often flip houses as a sideline to their regular jobs. They have the knowledge, skills and experience to find and fix a house. Some of them also have union jobs that provide unemployment checks all winter long while they work on their side projects.
The real money in house flipping comes from sweat equity. If you're handy with a hammer, enjoy laying carpet, can hang drywall, roof a house and install a kitchen sink, you've got the skills to flip a house. On the other hand, if you've got to pay a professional to do all of this work, the odds of making a profit on your investment will be dramatically reduced.