He didn't say "how". He said "who". You need to know who to talk to. When I was a mechanic, the salesmen in the shop barely knew the difference between a handlebar and the plunger we kept in the bathroom. They would frequently ask me which component was better, sometimes after they had already answered the question with a guess in order to make the sale. Of course, many customers just assumed that we all knew the same as each other, while the savvy people knew to only ask the people in greasy aprons turning wrenches.

And yes, as you're experiencing, some shops are full of people who know a lot, and some are full of people who only know how to push one foot down as the other comes up.