In my experience there are alot of RPI staff in London, who like Yorkie said, are badly trained and have atrocious manners. I'm not saying this is true of all of them, quite the opposite, but it seems the numbers of such people are on the rise.
Some of them do honestly think they are a god like figure, who cannot be questioned nor overridden. Several times I've had one try and tell me my ticket isn't valid, when I know full well it is. When I told them I had a copy of the ticket restrictions from Avantix NFM, they were usually quick to back down.
They prey on the fact that the your average customer will not be aware of such things, and will accept their ruling to avoid confrontation. I think it's atrocious that they, and by extension their employers, victimise perfectly respectable customers whom without they'd have no business. It's all in the name of greed, making a buck, and it is NOT acceptable.
The general consensus among alot of rail enthusiasts is that if you make the mistake, you are liable and you should accept the punishment. Tell me this, if you paid for a coffee, would you accept it if it was wrong? If you chose to not accept it, if they told you it was your fault and they did not make the mistake, would you accept that?
As a reprisal to anyone who may disagree, this is my personal experience as a commuter into London, who regularly deals with the TOCs involved. If you are a user of the same services, feel free to comment, but if you are someone from an entirely different area, who has little or no experience of these services, please do not comment.