InterNACHI Standards of Practice
Any association's Standards of Practice are a minimum guideline. Like building codes, they set a minimum standard of care. Many inspectors routinely exceed the minimum standard in order to provide their clients with a better inspection.
Those inspectors who choose to exceed the standards should be qualified and trained to do so. For example, it states in the SOP's that an inspector is not required to walk on the roof surface. I walk on all roofs, providing they are accessible and safe to walk on, which is most of them. I am a Certified Installer with the Roof Tile Institute and have been trained to walk on and inspect concrete tile roofs.
There's probably another 25-30 items excluded in the SOP's that are not required to be inspected, but I choose to inspect them because I am qualified to do so.
Many inspectors charge extra for a "Premier Inspection" which includes items disclaimed in the SOP's. I don't charge extra for similar items. I am of the belief that in order to perform a professional inspection, the SOP's must be exceeded and there shouldn't be an extra charge to perform a thorough inspection.