Lesson 0 has to be 'have several years electronics repair skills under your belt' - and that's the kicker for most.
I agree though - a bit of knowledge can be a powerful thing; a 'resistor pack' for my car (to regulate the 4 speed aircon blower) is 80UKP + labour to replace when it fails but the most common fault is that the thermal fuse (approx 0.80UKP to replace) blows when the airflow is reduced by an air filter that just needs a clean-out.
I agree though - a bit of knowledge can be a powerful thing; a 'resistor pack' for my car (to regulate the 4 speed aircon blower) is 80UKP + labour to replace when it fails but the most common fault is that the thermal fuse (approx 0.80UKP to replace) blows when the airflow is reduced by an air filter that just needs a clean-out.