There is nothing wrong about it, monetizing an even like that is just normal, because you are giving away your time and your service to people, for them to learn of course, and if they don't like it, having a seminar or meeting that is being monetize by you or by the event organizer, then they can just simply not go, easy as that.
Well, they ask questions both online and offline. And considering the fact it wasn't monetized from the onset, I just can't find it being monetized anymore. Tho I'm doing this for bitcoin too, the stress isn't easy.
And about this, you could always ignore them, you have the right to refuse to their questions, and there is nothing they can do if you don't really want to, they can't force you to answer their questions because that is pure harassment, you could call the police if they will reach that point.