I grew up with Newcastle ticket office which actually had and continues to have some very knowledgeable staff - though I seem to find myself in there about once a year these days. The last time I was there I found myself explaining a TADA (Travel Agents Discount)form to someone who's been working in there for a considerable number of years, and I was lucky that she had the patience and enthusiasm to sit through it with me and issue me what I was after. Even then - I'm aware that some staff there do get things wrong!
Meanwhile I spent my student years in Sheffield whose ticket office would make it their mission to be as awkward as possible - going so far as to refuse to issue tickets, refuse to do ToD when the TVMs weren't working properly and even complain about me to colleagues when I'd for something 'unusual' (in the last instance a panicked hand went over the microphone).
I've also had quite a number of ticket offices down south who just didn't know how to do something, didn't want to know how to do it and would get quite defensive if you asked. I was also accused of fare evasion by an extremely unpleasant man at Stroud several years ago when I asked for a ticket from a station that wasn't Stroud! Honourable mention also to Dartford station - I asked for a Boundary Zone ticket, was sold something else, then given a load of lip for making them refund it and issue me what I actually asked for.
The exception to this, as another poster has mentioned, is London Bridge - I asked them for a ranger ticket well out of area once and the lady behind the counter didn't even blink. Issued in seconds.
Put simply, it isn't worth the hassle most of the time. I don't want to debate with someone why they should issue me a ticket, or hear about how they've been doing a job for a certain number of years which automatically makes me wrong, I want a ticket and to be on my way.