Very seldom do I work on the underside of a playfield with the game switched on. I guess I do have the game on if the issue is a globe or just observing moving parts - like flipper EOS issues. But, I do all the adjustments while the game is switched off.

As a habit, I throw a towel over the on/off switch area - a habit I have when working on EMs. Throw the towel over the entire bottom section so that when I'm working on the underside of the playfield, no screws drop into steppers etc..

Any machine I buy (and I don't know it's history) - I check the plug. No ground wire ? Replace the plug...