The indie dev behind Factorio spoke out about the grey market resellers in their blog. They talked about G2A, where they had received a bunch of fraudulent purchases, and had to pay fines to the credit card processor for each chargeback... Effectively making reseller sales cost the developer money instead of earning it. Here's the 4 blog posts talking about the issue.

https://www.factorio.com/blog/post/fff-171

https://www.factorio.com/blog/post/fff-303

https://www.factorio.com/blog/post/fff-304

https://www.factorio.com/blog/post/fff-348