Here's one I see allot...The Sensei is far too "busy" to teach beginners so he directs one of the senior students to teach instead. Now every class is spent teaching the basics to the beginners.
Should the Senior Student be compensated?
Is that an assumption that the teacher is too "busy" or did they tell you that's the reason one of the senior students is showing basics to beginners?
You may consider another reason ... especially if it's done properly, the senior student IS being compensated by the most senior student in the dojo (the sensei) by teaching them how to be a teacher. I'm not saying that what you described doesn't happen; it's just not the only possibility.
About osoji in the dojo by people who pay dues... I won't accept anyone into the dojo that won't do osoji because that's part of the education. I realize that there are folks that don't agree and make the relationship of student and teacher a mercantile transaction. I don't think that's budo practice.