23 Degrees, are you using the word zoning codes and building codes interchangeably? Because a subject that has undergone changes structural or otherwise from public records might still have legal zoning, but be in violation of county building codes by not getting a permit for certain work done. Therefore, checking legal in zoning would not be misleading.
Zoning addresses the use of a property, residential or commerical, single family use or two family use, as well as setbacks and how many stories can be built etc. But zoning codes are one thing and building codes another.
In the case of the original post, the poster said the county had dual zoning allowed in the area, a structure could either be used as single family or dual family and either was allowed (not my area so I am assuming the poster reported that accurately). Therefore, the change from two family to one family is still legal under zoning, but the change did not get the proper permits from the building departments. The building dept sends out code inspectors who are inspecting if quality and methods of material, electrical and other factors on conform to code, and if the plans/specs and materials/workmanship and contractor licenses are all correct, they grant a permit. I don't think these same inspectors are also looking for how many families live in the house or if they are running a business out of the basement (zoning issues)
As to appraisers taking it seriously, I think most appraisers do. One of the measures of SOW is what are an appraiser's peers doing. If more appraisers take the view that we are hired to provide value opinions and are not home inspectors, which is the case, that is one measure of how seriously to take the issue of changes to a subject that is not permitted. You and a few others here are using HUD terms CB 3 etc to apply to non HUD appraisals. FHA/HUD specifically asks in the SOw that appraisers take on a partial home inspector role for certain visible defects. At the same time, both FHA and Fannie state in guidelines that if market shows value for non permitted improvements or additions, that the appraiser can relay that value in the market despite lack of permits.
IF an appraiser discloses what was done, any changes made from original and reseraches if it is legally allowed, even though non permitted, they are not producing a misleading report. It is misleading to pertend permits exist when they don't, or that the changes were there from original plans etc. As to potential electrical hazards etc from non permitted work, are we building inspectors? Is that part of our SOW? To date, it is not. If we see conditions that visibly affect value of property through causing a health and safety issue, we have to disclose it and that is cause for subject to, because it is such that would affect value.
No matter what, we can never predict the presence of unknown hazards in a home. Even with permits, a home can have shoddy construction, improper electrical work, radon, mold in certain areas, leaks we can't see etc. So where does it end? Should we also carry a mold detector kit and test air samples? A radon kit? What level of responsiblity are we taking, and should we be taking any of it, when it does not relate to the assignment, deriving an opinion of value?
When a roof inspector comes over, they don't start taking on other roles and adding to their report comments about traffic in the neighborhood and how the houses are being devalued. Appraisers are the only ones taking on un asked for roles that they have no expertise in and that their clients don't even expect them to do.