What do you mean by Single Presentation?  You may use one cartoon for one presentation.  If you have a seminar and you want to use the cartoon in that seminar, I see that as a Single Presentation.  Some people have seminars that cover two or three days.  Let's call that a Single Presentation. 

Example: You use a Will Street cartoon in your September seminar entitled, "Let Me Manage Your Money!" which is held on Tuesday evening and Thursday morning and Thursday evening.  Let's call that a single presentation.  BUT, when you have another seminar in December entitled, "Mutual Feelings about Mutual Funds" and you want to use the same cartoon, you will need to secure the rights to use it again.

What do you mean by Multiple Presentations?  You may use the cartoon as often as you like during the term of one year. 

So, what keeps people from purchasing a cartoon for a Single Presentation and using it Multiple times?  Nothing.  Will Street is very trusting of people.