Does anyone know what county assessors actually do when the residential and commercial components get assessed on the same parcel

Georgia assessors are required by state law to use fair market value as their standard, but the methodology behind a specific assessment is rarely printed on the notice itself. What you are describing, a single-number assessment on a mixed-use parcel with no visible allocation between the retail and residential components, is common. Whether the assessor used one approach or blended two is usually documented internally, and you can get at it.

The starting point in Georgia is a written open records request to the county board of assessors under the Georgia Open Records Act. Ask specifically for the property record card (this is the assessor's internal worksheet for your parcel, showing square footage, use classification, comparable sales used, income data if they ran an income approach, and the capitalization rate they applied). On a mixed-use parcel, a careful assessor will run two separate analyses and weight them, or pick the approach that best fits the dominant use. A less careful one may default to residential comps for the whole building because the apartments outnumber the retail bays by count or by square footage. The property record card will tell you which happened.

If the card shows a single residential comp set applied to the whole building, that is the number you would contest in an appeal, because retail income streams are valued differently from residential ones. Retail is typically valued using an income approach (rent collected divided by a market capitalization rate to arrive at value), while residential small multifamily often uses a sales comparison approach (what similar buildings sold for nearby).

I want to be honest that property tax appeal strategy gets complicated quickly, and if you get to the point of actually filing, a Georgia property tax attorney or a certified general appraiser who works in the state is the right person to review what the card shows.

What county is the building in? Some Georgia counties publish property record cards through their online assessment portal, which would save you the open records step entirely.