Home Inspectors must follow whats called a SOP (Standards of Practice). Every state and orginization has one. They differ from one another, but overall pretty similar.

Below are the links to the state SOP's that I follow or you can click on Standards of Practice on the menu to the left to read here.

WISCONSIN SOP:
www.legis.state.wi.us/rsb/code/rl/rl134.pdf

ILLINOIS SOP:
http://www.ilga.gov/commission/jcar/admincode/068/068014100C02000R.html