And still I would do it myself.
Where did his OS install come from?
Some years ago, in a BigBox store, looking at the return rack selection of PCs.
A prebuilt HP system, at a good price.
I ask the salesperson - "Has this system been fully reinstalled?"
"Yes sir!"
Later, I ask the manager - "Do you guys do a full reinstall on these?"
"Oh yes! We do a full reinstall on ALL systems that are returned" He was very adamant about that.
Later, when I got it home....
Poking through the Registry, what do I see. The original owners name, address, phone number, credit card num, etc, etc.
Just for the sake of verification, do it yourself.
Trust, but verify.
Full wipe and reinstall.
"Factory reset" only counts with a system from one of the major manufacturers. Dell/HP/Asus/etc.
Unlikely that is what you have.
And no, that is NOT the same as a wipe and reinstall.