Chatham is the biggest market this buyer works, and that changes the math a little
Chatham has more housing stock variety than the smaller towns around it — postwar bungalows, older downtown-adjacent homes, and newer subdivisions all in the same city. That range means the roof-furnace-wiring math still drives the number, but the starting point varies more house to house than in a smaller, more uniform town.
It also means more competition among buyers. A Chatham seller getting a cash offer should expect to be able to get more than one, and should use that to ask harder questions of each.
What to ask before accepting any number
What is the offer assuming about the roof, the furnace, and the wiring? Can that assumption change after a walkthrough, and if so, how much? What, if anything, comes off the number between now and closing? A buyer who answers plainly, in writing, is worth more trust than one who won't.