If you're intending to alter a motor vehicle that was put on the market with certain parameters which were considered safe and adequate to the car, no matter what reason you might have (improved mpg, improved performance or simple delusion), then yes, you need to educate yourself on the subject.
So why do that when tuning the car, but not when taking the car for a regular service/repair ?
Ultimately you're talking about mistrust.
There are people who get a remap by sending their existing map to someone, over the internet, who return their freshly tuned map via email, for £100 -£150. In that case you wouldn't expect the tuner to be responsible for very much at all, other than operating a map library.
Maybe I'm expecting too much to think that a tuner with a garage and maybe a rolling road would do more than that too ?
I definitely think there are differences in approaches and the tuners who do their own development work probably should charge more than people who load up off the shelf maps.
Is the price across the market too high at it's base level, well that's for the customer's to decide. (High price niche markets exist all over.) Talk of £50/hr labour charges being reasonable seem out of kilter with me. On a 38 hour week it's almost £100k per year, so maybe paying someone £100k per year to not even check the exhaust is clear of obstructions is where it sticks in my throat ?
Ultimately most tuning stems from the racing world, where the cost of winning is very high just to find the winning formula, and then repeating the formula costs much less on each iteration.
I realise I might have spoken a bit out of turn. It's not my money being spent at the end of the day, so all I've got is my free opinion !