In thetrout's scenario, I'd argue that having
TVM▸ 's at the destination station that can only sell tickets for the 'wrong' direction is
not an opportunity to purchase the ticket for the journey you have just made.
In this case it is the rail industry that has failed to gather the revenue, rather than the passenger failing to take the opportunity to purchase the correct ticket for their journey.
It'd be highly unlikely for a revenue block to be in place beyond either an open ticket office, or from someone with an
Avantix▸ . If there was such a block, then passengers who had travelled from a station that had no (or a closed) ticket office and/or a TVM set to 'card only' should be allowed to make their purchase rather than be Penalty Fared or reported for prosecution.
Of course it is also possible for TVMs to sell tickets from any origin - that's a software issue - but it's not a function
FGW▸ currently allows on its TVMs.
If, despite the rail industry's failure to offer you an opportunity to purchase a ticket at any point, you feel strongly that you must pay your fare, then you can always send the
TOC▸ a cheque or postal order. Or buy two tickets the next time you make the same journey.