About twenty years ago I was asked to make a presentation on calibration to a meeting of a local chapter of the National Conference of Standards Laboratories. There were a lot of newcomers to the industry at the time, some of whom were essentially kidding themselves regarding their abilities and too many trying to do the same thing to potential customers.
After an hour reciting a range of scams and errors that prevailed, the moderator asked if anyone had any questions. There were none, of course, as I had probably insulted over half of those in attendance.