[itamarst]

As far as content being posted for free, that seems hard to stop. One suggestion I've seen to reduce people actually downloading them in lieu of buying: https://successfulsoftware.net/2017/03/10/honeypot-page/

As far as stopping purchases: you can just disallow suspicious origins from purchasing. E.g. if you know it's Amazon IPs, ban those, very few people will legitimately do that.

[desperado]

We do ban those via Radar on Stripe... but there are so many... it's impossible to list them all.

[itamarst]

Some quick Googling suggests there are services to help with this, e.g. https://siftscience.com/products/payment-fraud (no opinion about this or any of them.)