TOPIC: Drill holes in furnace ducts?

4 years ago when I had my home inspected before buying, the HI used an awl to punch through the ductwork...I was not a happy camper and made that very clear to him.

I also use an IR thermometer and extending mirror to check as much as I can on the furnace...

That's an old technique Casey, and the thermometer looks like a mini meat thermometer.  The old-time HVAC techs used to stick it in there and watch the dial.  Your guy may have been a former HVAC pro and that was the only way he knew how to do it.  Wouldn't be so bad if he had a roll of aluminum tape to cover over the hold.  The really experienced guys drilled a specific hole and when done put a small rubber button inside that could be removed and re-used each time they came back to service the system.