If you had a CPA with Amazon, and the customer bought a book, then came back later to buy a DVD, would you be entitled to a 2nd CPA? Probably not.
Or if youi had a CPA deal with a travel company, and a customer booked a hotel room, then came back later to book airfare or a car rental, would you be entitled to a 2nd CPA? Probably not.
Seems simple to me. If you don’t like the terms of a CPA deal, don’t promote it. But unless they tell you they’re going to pay you a CPA, then they don’t pay it, no one’s been “screwed”.