Eyeballs, common sense, 30 years of buying and selling property, managing my rentals, being personally involved in a total burn out when I was asked to opine an as is value for the bank when the insurance company was denying the claim because the adjuster determined "inappropriate and non permitted" electrical upgrades, common sense appraisal 101 knowledge that condition affects value, dozens of lender and underwriter requests over the years to make a comment on the permitting process when an addition or renovation was mentioned in my report. I'm sure there's more but this list should keep the naysayers busy trying to tell me I'm wrong.