Yes, the engine would run like garbage with bad pistons...
If one got a tiny little chip, that managed to escape through the exhaust, then you'd probably never tell.
Best thing you can do is say "hey, im interested in the car, but I need to pull the spark plugs, or I'm going to walk away"
And if they say anything about it, explain that it's pulling spark plugs, you'll do 1 at a time, and they can watch to make sure you dont mess anything up.
If still no, tell them thank you very much, and good luck to them, then walk off.
