I use my GNE key card at least 4 times a day, and I've very rarely had any problems, apart from the first month of the launch. Nobody should be made to pay, because even if the ETM gives a "travel not allowed" error, the driver can run a report and see exactly what tickets are stored. My only gripe with that is it shouldn't be up to me to tell the driver to do that. I've never yet had someone to offer to do it without prompt.