Also, make sure you are staying within your target neighborhood - don't cross double yellow lines on the road.Taking all your comps into account, multiply the square footage of your target property by the average price per square foot of your comps.

I looked at the tax site to get my square footage, assuming that these sites are usually correct.

The Zoning Ordinances are typically the first roadblock, as depending on the Zoning Designation of your lot, and the overall square footage, you will be limited to a Maximum number of units allowed.

Square footage, eave height, roads, parking, etc.  

If you're that concerned, measure the footage yourself.

If you add square footage, increase bed/bath counts, or do a panel upgrade, 100% get a permit.

And if my client were to add an egress and therefore an additional bedroom and 600 sq ft of finished space, would an appraiser consider this similar to adding a bedroom and sq footage on the main floor or would they value these additions less because they're in a basement? 

Can you tell me more about your home (approximate square footage, bedroom/bathroom count, year built, basement, garage)?

But just down the street a 4/2 sold for $300/sq ft (similar overall square footage, nowhere near year built 🫣).

Square footage of our unit was about 1500ft2.