I used to try and explain it to them but it's like talking to a brick wall and when I go to the back and see the worn out breaker panel feeding everything I just give up. One time I was recovering refrigerant from a burn out and my recovery unit was bouncing all over the floor. After some investigation I discovered that the outlet the equipment was on and I was using had 240 volts going to a 110 outlet!
I've run into that a couple times where there is 240 on a 110 outlet. Sometimes I get paranoid, and check the outlet with my meter before I plug into it.