It's not really hard but it certainly is an inconvenience, especially if you're going to rip off a video game dev. It would take a lot of dedication and resources to exploit OP's policy, and pretty much no one would do it is the point.
I would also think that in cases like this you’re dealing with an indie dev who you’re never going to purchase something from again anyway. Steam would never have a refund policy like this, so the issue becomes moot.
It's not really hard but it certainly is an inconvenience, especially if you're going to rip off a video game dev. It would take a lot of dedication and resources to exploit OP's policy, and pretty much no one would do it is the point.