Unfortunately, it is usually the big ticket items that are overlooked by novice flippers. That includes the need to completely rewire a house, replace some or all of the plumbing lines, and repair or replace HVAC (heating, ventilation, and air conditioning) systems.
Electrical is a common problem because of the building inspection system used in most cities and towns. If you obtain a building permit in order to make minor repairs and renovations, the inspectors are allowed to inspect anything else within eyesight of the areas under repair or renovation. Almost always, an inspector sees something suspicious about electrical wiring and then requires you to bring the entire system up to current code standards. Another route to the same upgrade is when the fire marshal does a fire safety inspection at the completion of your project. If you cannot pass because of electrical deficiencies, you will have to spend additional money.
Finally, many people neglect inspecting the foundation of a house. Especially if it is built on a basement or a crawl space, you may have significant settling issues. That problem can usually be remedied with the installation of supports, but it is not a cheap fix.
To avoid being a sad story in someone’s flipping book, be sure to obtain a complete house inspection before your purchase contract becomes final. Before hiring an inspector, make sure he or she will advise you of building code deficiencies, not just things that do not work properly. All the electrical in the house might work perfectly, but that will not help you if you still have to bring it up to code.