Would have thought Google would be on top of this though, but probably not?

It’s against play store ToS, but if somehow you can make it look organic enough it might be difficult to proof. In truth I don’t know how this kind of services operate. I do think Google would try to counter this as much as possible yes. And 8M reviews can’t be just from this kind of services, at some point you have real users engagement, you just need the initial visibility boost.

Good luck with your research🖖