At Modern Pinball no-one seems to have a problem with pointing out an issue with a machine.

Some point out issues as if you caused the issue to happen to them on purpose.

Most want you to stop working on a machine to fix the one they are playing YESTERDAY.

Some point out issues more than others, much more than others, as they find something wrong with any machine they play.

Had a guy come over to me just yesterday complaining that the machine Tilted on him when he shook it!!!!!!

Many more complain about a LOCKED ball as being stuck!!!!!!!!

However, I appreciate it when someone finds something wrong and try to correct it right away.

Typical are complaints that a machine isn't level and I have to prove to their unbelieving eyes that it is .

Once I had to stop working on a machine as the player was insistent that the machine he was playing was not level. I used 2 different levels on two points on the playfield to prove him wrong. The guy didn't believe the results or the levels and used his own iPhone leveling app and it showed the machine was perfect and HE still grumbled that it was not.
He then took a ball in hand placed it in the center of the playfield and released it. It drained dead center between the flippers . He said under his breath "I don't know" shaking his head. I could see he was still not satisfied but decided to deal with it.

Bottom line is if an operator does not know that a problem exists they can't fix it so please inform them but please do so in a nice manner.