I've released a game on Google Play about 10 days ago - it's a port to a successful game on iOS, and it's been getting great ratings and reviews. In it's 25 first reviews it averaged 4.8, having only 4* and 5*s, and most of them not anonymous: people would type something like "great UI, smooth gameplay, etc".
Then suddenly in a matter for 1 hour, without any new updates or anything, I get 4 new 1*s anonymous (no text) ratings. Then the next day I get 3 more anonymous 1*.
I heard Google has some algorithms to check if things like that are happening and prevent it, but I assume it will only fire up if there are hundreds or thousands of fake ratings. But for a small app, a dozen bad ratings are already a big damage (rating went from 4.8 to 4.0, and falling).
So, any ideas?