DIY Fixes
There are a swath of DIY fixes that most contractors (like plumbers) don't want you to know how to do.
One reason is that some fixes can be dangerous.
But another is that by failing to know how to do something simple and painless, like turning a knob on your garage disposal or buying a better plunger, gives them a chance to charge you a lot for an easy fix.
They don’t want you to know how to do it yourself because if you did you wouldn’t be asking them to do it for you.
So the question is: are they doing you a disservice because you're clueless? And I think the answer is no.
We all have jobs, we all have lives, and we can't absorb all the information available. So someone charging whatever amount to solve our problems is fine, as long as we get what we paid for.
That's how every service makes money. It's likely how you make money too.
We pay to have our problems solved, regardless of the true costs of fixing them.