I've had several positive experiences in electrical and plumbing, where I was looking for a specific part and they were able to find it in a fraction of the time it would take me.

I've also gone in with "I need a fitting to go from (size and type of thread) to (other material pipe)" and had someone enthusiastically figure out a couple ways to do it, trying to find the cheapest/simplest way based on parts.

I know one of the people I had this experience with was a retired electrician, but I would bet that finding and keeping people with that type of experience is difficult.