We have had an issue recently where a pass has been buying a high value weekly season, signing for it, then geting their bank to do a chargeback on the ammount each week. The passenger is now being hunted down as they owe us over £1000 in fares. We have had the same attitude of a previous poster where as long as the pin has been entered correctly, a 'type in' could be done, but this recent case may change that.
As I've said before in other threads on cards, you see the same cards (and sometime the same people) whoose cards decline again and again, and even know some people who are happy with this as when the card is signed for after the original decline, as it takes longer for the TOC to take the money, as they are broke when the original journey is made, but will have cash in later.
And I've said before, there are people who look for 'weak' conductors who are happy to take payments without a pin for large tickets on unknown cards. I've turned down large ticket transactions like this, where the the buyer was not that bothered, knowing someone, somewhere would do the ticket, no questions asked.