I've spent a lot of time in HiFi shops when I was young.
I've also been working in some myself.
I strongly disagree with the fact that people don't want to be educated.
They of course don't want you to show a paternalist or condescending attitude, but that's very different.
And they don't blindly trust shop owner either.
What customers want is to be guided, because they don't know, and internet is of no help.
That's why they come to a local shop.
And to be able to see, hear, and touch the equipment (in that order, I think).
That being said, what other objective value could you bring to customers that you will be able to value ?
Meaning: that won't pump all your time, to see the customer ultimately buying from internet for a cheaper price ?
After sale service is one, but not that important (and costly + random, since you rely on others for the quality and speed).
Loudspeakers (and headphones) listening is key, in my opinion.
Installation and room correction in situ is paramount as well, of course, and should be emphasized. (And this kind of service is very high end.)
Proper advice for music source / way of distributing it is also worthwhile.
Also, partnership with domotic company may be great added value with higher end customers, IMO.
Tuning and set up of turntables, if that's what sone customers want, can be a key differentiator, since that's all but easy.
For electronics, how to earn (and not loose) money ?
Reputable brands with good electronics but high ease of use will allow you some premium price.
You probably don't need (nor want !) to keep 100 references in stock, and you may explain your choices by measurements and objective reasons, for sure.
Showing customers that you're able to reproduce the measurements in house, in some basement secret lab, would, for sure, give some credit to your assertions.
Position yourself as a helper in the seek for better audio value, by organizing blind tests, and educating people on hiw to compare and what to listen to.
Be convincing by being an advocate of objectivism, but always allow audition to confirm.
Because people will want to listen, anyway, and if don't allow it, they won't trust you.