Just offer your exam questions through me, no hidden costs or fees and you keep 70% of all your sales. That is the simple “no worries” model if you don’t want to deal with customers and go through the hustle to deal with the different platforms. You will get your own author description along with your material so you get all the credits for your hard work.
Get your own version of QuizzerWiz out there, rename it and offer it on all platforms for download.
This is the more personal approach since it gives you more opportunities to create a customer base and monitor your students behavior. Depending on the complexity of your requirements this offer comes with different price models and depends on the number of platforms and extra services your need (like backend functionality, design help or a support website for your customers).