That's my violent side coming back out after many years.
I've just been to take another look at that scene in the Smirky vestibule, and Nat certainly seems to get into a proper worry after Treguard's comment. He checks his notes too, to see if they do have anything they could possibly give him for the ride, but of course they don't. Smirky just admires Ben's "natural skill", I guess.
There's an uninformed comment on YouTube that says something like "well, there ARE free Smirky rides in other episodes, you know!", i.e. claiming there's nothing suspect or unusual about this situation. However, this really is unique as the only time Smirky gives a totally free ride BETWEEN LEVELS without some form of incentive, be it a physical fare, a set of questions answered correctly with Brother Mace, a token presented to the Gatemaster, a piece of flattery, a warning about the Brollachan, or a direct instruction from Elita or Romahna.