The only way to 'make things fairer for everyone' is to make sure that all passengers pay the correct fare for the journey they are making. The yellow card system would require all fare dodgers to be positively identified and their details recorded on a database accessible by all relevant on-train staff. Best of luck with that. It would be far better if the rules were changed so that 'honest mistakes' were dealt with by making the miscreant pay just all or part of the fare as appropriate with penalty fares and reports reserved for those obviously engaging in fraudulent activity. I would venture to suggest that most railway staff concerned could spot the difference in virtually all cases.
"Obviously" doing some fairly heavy lifting there?