I understand what you are saying, but what if when you listened, you heard differences? This is often what happens, and when those very well meaning folks are challenged to use a more precise method of measurement (multimeter), we get the 'Nothing is ever good enough' line or something similar, which tends to discourage much further.
This just reduces the likelihood of disappointment when results are inevitably questioned.
It really is better to start with an easier, much more accurate method that then removes any doubt about that variable at least. When I tested myself, I figured that if I 'passed' I would need to enlist the help of someone to be able to make it a double blind test, but it never got that far. Because the level matching is SO important, it really needs to be the first thing on the list to get right.