Fair comment, but I like to think that I have been able to tell between the good and the bad, especially if you see more people for comparison - even when I was young. I mean, I'm not very good at soccer but I can easily see who is and who is not good. .
Perhaps you're unusually astute, then? I say this because there are plenty of garbage "martial arts" schools whose students are fervent fans of what they're doing, and who earnestly believe that they're being taught good stuff by good instructors. If it's a common skill to distinguish good from bad, even with no prior experience, how do you explain these students?