That $7 plunger trick actually works pretty well for the right kind of dent, the shallow ones on a flat panel where the metal hasn't creased. My uncle did it on his old truck door with a plunger he bought at a True Value and it popped right out, looked decent enough for a beater. I get why your boss called it a hack job though, cause body shops hate it and honestly if the paint cracks or the metal is stretched it can make things worse. But for someone who just wants the dent gone and doesn't care about it being perfect, spending $7 beats spending $700. Sucks that he gave you a hard time over it, you were just trying to fix your own car without getting ripped off. Maybe it's just me but calling something a hack job says more about him than about your plunger.

Mesa heat cooks those ground straps every July, so after two summers of dead Silverados I check grounds before I even plug in the scanner.