If that is a purely technical feature that can't be marketed from business viewpoint easily, use prototypes or samples to demonstrate, walk them through the process you intend for them by explaining your vision.

If you're not working with some specific customer (but just throwing the product online and hope someone starts using it) then you better find at least one live, cooperative customer to work with (huge discounts or even for free if necessary) and see your own product through their eyes. That will help you understand most problems with the product or marketing.