I don't think anyone would want to be sold a ticket that wasn't valid. I can't really see the relevance of your question.
The point is that it's none of the clerk's business what the intended journey is, so given that he doesn't know my plans (and shouldn't make assumptions), how can he judge whether the requested ticket is valid or not? If I go to Shipley station and buy a ticket from Leeds to Doncaster he should not interrogate me on how I intend to use that ticket. He should sell me what I ask for and if I use that outside the validity of what I've asked for then that's my fault. He can advise (if asked), but should not intervene in any other way.
I think 'interogate' is a bit harsh frankly. Passengers want the cheapest fare and when they do ask for a specific fare, in my experience, I would say the majority aren't actually aware of the restrictions and ask for the wrong fare. What you are saying is that I should just issue it regardless of it being valid. I think that is the wrong attitude to have.
Many people ask for 'open returns' because they want to return at any time that day, but what they actually want is an Off-Peak day or Anytime Day return, which is often substancially cheaper. When they ask for an 'Anytime Return to Manchester Airport, I often comment that singles would be cheaper in most cases and certainly no more expensive. Yet in both these situations you think I should just issue the specific ticket.
Now I will say that I personally have never refused to issue a ticket, but that doesn't mean that I should blindly issue specific fares when requested.
Also, if both parties know the ticket is not what the passenger needs or even if it is just the clerk that knows, where does the responsibility lie? If the passenger gets on a train that the ticket isn't valid for, do you think they will say 'oh I didn't realise, it was my fault because I asked for the specific fare and [they] have to sell it'? or is it more likely they will say, 'the clerk didn't say it wasn't valid'?
I think the difference depends on what you ask the clerk for. If you turned up at New Street and asked for 'a ticket to London', you'd expect to be given one valid there and then, from New St to London. If you went and specifically asked for a SOR from Coventry to London, you should be given that, no questions asked, even though its not valid from New Street - because you have specified a particular ticket....
But what of 'open returns' and 'savers', in my experience both have been used to ask for Off-Peak Day Returns.
....I know of ticket office staff who will sell anything you want, but merely ADVISE that it won't be valid - this seems like an ideal compromise to me, because the customer's right to buy any ticket they ask for is preserved, but there can also be no claim of ignornance of the rules on the part of the customer. For example, somebody who insists on an off-peak ticket before 0930.
It's a fair situation, and often what I do. It alerts the passenger to potential problems whilst 'giving them what they want'. When I have done so and it turns out the ticket is not valid or not the cheapest fare, often the response is some remark about 'the website being wrong' or 'why did the website say...' or something like that.
I have asked if people have tickets to get to the origin, or how they intend to get there and in those cases, and when they are travelling by train, they have had no problem with showing the ticket
without being asked for it, or have asked if I want to see the ticket and producing it. I personally wouldn't demand to see it, although I've never needed to, but again, there is no reason why we can't if it is relevant ticket.
