A home inspector is trained to be a detective in regard to the construction and working parts of homes. It is not an exact science.
The home inspector cannot tear into things, so they can’t always see everything they’d like to. They do, however, come equipped with ladders, strong flashlights, and devices to measure various things related to plumbing, electrical and other necessary home items. Importantly, a home inspector will also typically bring a digital camera to photograph problems such as roof shingles not lying flat, signs of mildew from leaking pipes and construction that doesn’t comply with building codes.