Inconsiderate engineering

I had a 1973 Mercury Capri I bought new that had bad valve seals. It didn’t severely affect the oil mileage so I ignored it until I went to sell the car and everyone was concerned with that puff of smoke at startup. I got all sorts of high prices to replace the valve seals with everyone talking about removing the head. One guy was so much lower than the rest I asked why. The answer was he’d screw an air fitting into the spark plug hole and pump 100psi compressed air into the combustion chamber. The compressed air kept the valves in place while he replaced the seals. It made such sense I let him do the repair and it came out great. A few years later I used his repair trick on a car myself and it worked like a charm.