if you are very good at it and will show results, i offer % from our market profits.
if I understood correctly, you are not offering a guaranteed payment here but only a percentage of potential earnings?
if that's true, I think you'll have a hard time finding the right person for it. Any SEO expert will run his own service and get 100% of the profit rather than expect something from you.
Just to clarify i will pay a market rate for the services just want to have guaranteed results which is not unreasonsble. But if i could find a seo expert who wants to collab and share profits that will be welcome as well