Roland Perry wrote:

I dunno, but from conversations overheard on the train I get the
impression that a lot of tourists dodge the Schiphol-Centraal fare;
either because the machines defeat them, or they "genuinely" think they
can buy a ticket on the train.

There aren't obvious notices stating that you can't on display, and
it's accepted UK practice that unless there is a barrier check or
penalty fare scheme (the latter being well-publicised in most cases)
that it is acceptable to pay on the train so long as you want a
full-fare single, just as it is in Germany (with a surcharge).

There's always the ticket office at Schiphol (though there is a small
surcharge).

All this suggests to me that while NS is operationally very efficient,
it is highly customer-unfriendly.

Neil