We made a reservation for two people of their tour just shy of a month prior to our visit, as their website promised a discounted rate for advance bookings. When we arrived, however, we were told that the person that took our reservation "doesn't actually work here". In fact, when we first told them that we were there for the 10AM tour, the operator's response was "Oh, another one of those" - implying that this problem was not specific to us.
Since they had apparently cancelled their 10AM tour, they offered to accomodate us on their next tour at noon, but as we had a long drive after the tour, we couldn't afford to waste two hours.
We went to the neighbouring booth (Captain Mark's), and they were able to accomodate us on their 10AM tour instead.