Those all sound like they could be genuine mistakes. At least the passenger bought a ticket in those cases!
I'm a bit wary of discretion, as if overused it can end up with one rule for one passenger and a different rule for another. As an example, I witnessed an RPI let off a middle-aged woman who had a ticket that was clearly invalid, and couldn't help thinking that had it been a young male with a hoodie on the same train with the same ticket, that it would have been more likely to be prosecuted.
The direction of the conversation is usually determined by the passenger's attitude as opposed to their looks (except for vulnerable people).