There are two paths that I think are followed:
1. Knowledge about circuit behaviour and fault conditions leads to a desire to measure for the presence of these fault conditions. With specific tests in mind, and an understanding of the limitations of those tests, a tester is purchased and operated. Each test can detect the specific common faults we have though of but will not detect a smaller subset of more exotic dangerous conditions we haven't though of. This is the thinking like an electrician path and it probably leads to greater safety.
2. A test appliance is purchased and operated with the hope that the test appliance can somehow make a safe/unsafe decision. I think this path probably leads to greater danger.
I try my best to do the #1 path and also set up failure scenarios on my test bench to measure and analyze what is actually happening under strange wiring situations. If you assume that everything is wired correctly and 100% to code, then you could be making a deadly mistake. For instance, RPBG (Reverse Polarity Bootleg Ground) outlets should NEVER happen. But in old buildings wiring shortcuts are often taken either to save money, or simply because a DIY guy didn't know any better. That's what makes older church wiring so dangerous. Many times receptacles have been rewired by church volunteers who have no knowledge of electricity and certainly are not licensed to be doing electrical work.
A lot of my RV readers do the #2 path and simply want to plug in something like a SurgeGuard voltage protector to give them a confirmation that everything is wired correctly at a campground outlet. Unfortunately, there are no RV voltage protectors that will detect or disconnect an RV from the hot ground in an RPBG outlet. Still, these same readers will insist that they don't need to measure any campground outlets since they have a $300 black box on their shore power plug that protects them under all conditions. I also did a gig with a guitar player who claimed that his $100 surge strip would protect him from getting shocked, even though he had the ground pin broken off of its power plug. Nope, not a GFCI, just a fancy surge strip with RF noise filters. That's just crazy, but he believed it. Yikes!!!
I did a survey 2 years ago on PSW which revealed that 70% of the 3,000 musicians and technicians who answered had been shocked on stage or by sound gear at some time in their career. We tend to accept getting shocked as just part of the business. But every shock is an indication that something is seriously wrong with the wiring somewhere and it's time to get out the meter for a closer look. Of course it would be far better to be proactive and find wiring problems BEFORE they shock and possibly kill someone.
Keep fighting the good fight for electrical safety and understanding. And NEVER accept getting shocked as normal.