IMHO, the best that we can do is give each individual instructor the option to create a list of people who cannot sign up for his or her classes. Even that can be circumvented by a deliberate troublemaker with throwaway e-mail addresses.
Assuming that not marked is a no-show is incorrect because the instructor sometimes/often does not bother to check roll when there is not three or more present. It would be unfair to ding a student because the teacher did not take roll.
The only real solution is to do away with honorariums altogether, but that will never happen.
Cancelling if nobody signed up is one thing, but if at least one has registered, the instructor should follow through even if only one showed.
Even if nobody registered, the tool and classroom are still blocked for most of that time until the class is cancelled. I would rather the resources get used for a class of one or two than blocked from other instructors for a class of zero.