Unfortunately if you want to push your knowledge base and spare parts stock into the 95th percentile, you won't easily find the income to cover it.
(Or the stock, when you need it

)
Nope, the shape of things to come is already here.
I was restoring an old funny bike, and I walked into a bike shop and told the kid I needed a 650c road tyre.
He laughed at me and said "No, road tyres are 700. 650 "B" is 27.5 mountain bike. There's no such thing as 650 "C"." Then he shook his head and laughed again.
Obviously the little snot had never seen a triathlon bike or a junior road bike with 650C wheels, but it was clear that he had never seen anything older than the previous Tuesday.
Rather than waste my time educating the little house brick with acne, I walked out. He probably still tells his friends how HE educated ME. Sigh...
Shops like that are the reason I vowed never to restore something with a French or Swiss BB standard.
Many bike shops of my youth were run by incredibly grumpy old men - but nowdays an arrogant kid isn't an exception.
But to tell you the truth, the required levels of customer service, patience and aforementioned knowledge are very high, yet the cost of retail is so steep it's hard to retain staff with a decent wage,
there's almost no prospect of career progression and the industry spends most of the time screaming about how it's about to fall off a cliff.
An additionall point, speaking as someone who's employed say 30 mechanics/ shop workers over the years:
A natural mechanical ability, and
A friendly customer service manner
...aren't necessarily found in the same person.
Loads of people think they know all about bikes, when their knowledge is in fact restricted to a small segment.
Some of these people are behind the counter.
It's a case of the
"Unknown Unknowns"
, as Donald Rumsfelt helpfully called it.
You does what you can.
Sometimes it's enough.