I think #1 is a bit of a red herring. The security problem is not what this is solving. It's the ease of getting paid for some content, with less hassle overall.

Keep in mind that this is digital content so anyone could just rehost/resell/redistribute anything they bought or downloaded. But for something low-payment enough or the average silly download, why would they bother?

It's important to tell sellers that it's insecure so they don't assume it's locked, but please don't complicate this by adding DRM or sharing prevention. The most I'd do here is track downloads and let people kill their link and repost it if they sense abuse.