Just listened to a bloke get shirty with the train guard - he had an advance ticket for a different train, not valid on this service, so he had to pay full price.
It isn't the guard's fault - it says quite clearly that the ticket is only valid on a particular train. And no point complaining about cost - trains are pricey, that's why people buy advance tickets!
Every time I have travelled by train recently I have heard the same bloody argument!