The add-ons are real scope, not padding. A standard home inspection is a visual, non-invasive look at what the inspector can reach and see on the day: roof, structure, exterior, plumbing, electrical, heating and cooling, insulation, interiors, and the built-in appliances. Nothing gets opened up, nothing gets dismantled, and anything that needs a different tool or a lab is outside it.
"Standard of practice" is the written scope the inspector works to, published by a professional association or set in state rules where the state licenses inspectors, and licensing and scope both vary by state. It's the document that says what a $450 inspection is and, just as usefully, what it isn't. Your radon test needs a device left in the house for days and a lab reading. A sewer scope needs a camera down the line. Termite work is a separate discipline and in many states a separately licensed one. None of those are visual, so none are in the base fee.
The detached garage charge is the one people push back on, and it's simply more building. It has its own roof, slab, and often its own electrical panel.
One thing to look at on that sheet: the inspector's own limitations section, the part listing what wasn't examined. Wet crawl space, snow on the roof, a locked electrical panel. Those lines are where the real unknowns live after you've paid your $990, and buyers read the summary of defects and skip them almost every time.
