If this is not a free game as in FOSS, I'm not highly sympathetic.

Basically, this sort of thing is a way of collecting money outside of the store. Bad agents can disguise "in-app purchases" by handling them via a "donations" page.

It could easily be that donations are actually payments, because users who donate have some sort of preferential treatment in the software.

If you run an operation like the Google Play Store, you cannot investigate everything into that level of detail.

Next time, try having an unobtrusive link to a general website, without insinuating that it's a page where you pay.