How do i guaranteed my cut in a work contact?

[Elvira Longoria]

I have recently agreed to be a property finder for a wholesaler to get 20% of his assignment fee on any successful property I help him wholesale. Seeing as how this would be my first time partnering up with someone, i would like to draw up some kind of agreement contract assuring the percentage i would be owed if he manages to successfully wholesale to one of his buyers. I only have one question: is there any way to verify or write into the contract a way to see how much his assigned fee was? Otherwise, I would only be relying off of good faith to get the cut i am owed. Does anyone have any thoughts or similar experiences to add from?