As an observer I see 3 possible scenarios.
Seller wasn’t truthful.
His gauges are not accurate. I think you demonstrated that yours are.
His compression test was done at different rpm than yours.
All the drills I have are 2 speed.
Low speed is too slow to give an accurate reading and high speed
would give an excessively high reading.
As I don’t know how the both compression tests were done, this
variable doesn’t allow me to support either side.
Tubs.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.