So Brad, what, if any legal forms do Auditions sign specifically stating that your company may use, without compensation or acknowledgment, in perpetuity sans liability any or all aspects of their interview to create or improve products or services to the exclusive benefit of said company?

Great way to conduct product research for free.

Unless...

--- the process standardizes your auditions such that you test applicants experience on a product or service already in play in multiple markets.

Slowly, over time, folks discover their time, experience, expertise is worthy of some monetary compensation. What they choose to charge directly relates to their sense of worth.