Do You Run Seminars, Workshops, Or Conferences? Quick Question.

I have a question for those of you who are involved in running
your own seminars, workshops, and conferences.

I run a seminar business here in Boston, and have a local lead
pool of just over 500 people. Every month I run 2-3 seminars on
my particular subject, and I occasionally bring in outside
speakers to present to my group. In exchange for them delivering
their expertise, they get to sell their products at the back of
the room at my seminars.

My question is... how do you handle the profit split? The way I
did handled it at this last one was that I kept all the ticket
sales and let the speaker sell his book and keep all the profit.
He also pitched a back end seminar in which I get a cut of the
profits.

Here's where I need some specific guidance.

First, does the fact that he gave my audience two hours of great
content and I kept the ticket sales entitle him to keep 100% of
the back of the room sales, or should I still expect a cut of
that profit?

Second, I own the reprint rights to the book he was pitching (in
exchange for writing the sales copy on his website to pitch said
book). When he's not presenting to my group, is it reasonable to
assume that I can print up copies and sell them to my audience
and keep 100% of the profits even though he occasionally pitches
the same book to my readers?

He still makes out on the back end with his high end seminars
(which I still get a cut of), but I want to make sure that he
doesn't feel that I'm taking advantage of him (and I want to make
sure that I'm NOT taking advantage). How does the profit split
usually work when it comes to bringing in speakers to present to
your audience that you've worked hard to build up? Thanks.

Jason