I'm still left unclear how a member of the public is meant to know which stations will won't sell advance tickets.The relevant National Rail webpage
http://www.nationalrail.co.uk/times_fares/purchasing_tickets/ has links for which stations have ticket offices and what their opening hours are but nothing I can see about differentiation between ticket offices.
With all respect, whilst I can see an issue where a station doesn't have the right equipment (although one would have thought that providing such equipment is a pretty basic issue for a TOC) its very difficult to see why pay levels should come into the equation these days. As all of those who book on-line prove, selecting an advance ticket is scarcely a complex task.
Whilst sympathising with those who work at stations with limited staffing, from a passenger viewpoint it seems a poor reason to refuse to sell an advance ticket, especially if its a station that's designated to sell them. A shop that said 'please don't buy that here even though we sell it' wouldn't survive very long. Again, just what are passengers meant to do?-use guesswork as to how many staff will happen to be there at a given time?