A fairly common mistake people make when buying a home is to trust the appraisal and seller's inspection rather than hiring their own inspector to represent their best interests. An even more common mistake is to not understand the need to maintain an ongoing relationship with an inspector for ongoing service as it is needed.
Selling a House
An inspector is essential when selling a house as it allows to identify and repair problems before a potential buyer finds them and uses the knowledge to give a lower than expected counter offer. The inspector also provides for the moral imperative in which you know you're selling a great home in good condition to the new family who will be moving in without the expectation of having to conduct immediate repairs.
Buying an Investment
Although you take pride in selling a great home, investors aren't always ethically tedious about their dealings. If buying an investment home, whether you plan to live there for a few years while saving for a nicer house or if you intend to put some work in and sell for a profit, you need to understand what you're getting into. Code inspectors are only assuring the building meets minimum requirements and an appraiser only tells you the value of the house. Hiring an inspector to work on your behalf gives you an actual idea of what work the house is going to need immediately or in the near future.
The Ongoing Problem of Radon or Carbon Monoxide
Radon can leak into the basement or crawl space any time during the life of a house. As the house settles over time or as minerals in the ground underneath break down, radon can begin to leak into the home. Carbon monoxide is equally dangerous, and can begin to form when appliances get older and begin to function less efficiently than their design plans call for.
Mold and Moisture
Anytime excessive moisture is introduced to a home, mold will begin to form. Ideally, an inspection can prevent the problem before it occurs, such as identifying a potential leak in the roof or foundation or a weak spot in a plumbing fixture. Once mold does begin to form, it needs to be stopped immediately as it only spreads and becomes more expensive to remove while causing health problems which get worse over time as well.