I don’t know if this would work, but what if you sold something digital to someone and hashed it with their credit card information such that it would be perfectly usable on any system?  Anyone could use it anywhere at anytime. They could pass it around and share it with everyone in the world. But, if they shared it with others, they would be passing along their credit card information at the same time.  So maybe they wouldn’t want to share with others so readily.