He is not penalising them at all. If they have not paid the correct fare for the journey then he is acting as he should be which is professionally. If he had £1 for every person that claimed to have been sold the wrong ticket then he would be a millionaire. FIRST response from anyone who is knowingly travelling on a non-valid ticket by train or time is that they were not told they couldn't travel by that train, or they had been sold the wrong ticket. I have seen people go and buy (ask) for a cheap day return and then get on a barred train a claim they had been sold it and not told, or were told it was valid when they had not. Ticket issuing staff doing the job day in and day out rarely make mistakes of such proportions. The Guard technically does not have the power to alter the rules applicable to tickets, although he may exercise a degree of discretion depending upon his reading of the situation. At the end of the day it is for the passenger to ensure that his ticket is valid for the train and the journey he proposes to make. If he has a dispute about the ticket he was sold then it is for him to put his issue in writing to the relevant TOC. In Law the Courts assume that the passenger has taken reasonable steps to ensure he has the right ticket. This can happen if you go to the check-in desk and your ticket is not correct for the remainder of the journey. The only difference with an airline is that this happens before you board. How is the Guard to know it is a "staff error" ? Take your word for it ?....Yeah right, as I explained before one of the many excuses used by those travelling wrong is that the wrong ticket was sold, i. e. "staff error" simply because it is very hard to prove. It is not the Guard's job to act as judge and jury, he should simply rectify the situation and you should then take the matter up with the TOC. You are NOT being penalised because generally you are only being asked to pay what is the corrrect amount for the actual journey being undertaken. That is not a penalty. Tell us how you discriminate fare dogers who tell a guard they have been sold the wrong tickets as against someone who has been ? And how far does discretion go ? What become the new line at which the Guard applies the rule, and why at THAT point ? why not somewhere else, because ultimately someone has to have the rule applied, or we don't apply the rules at all.