You would be surprised. I was shocked when well-funded competitors did this to us (and other strange smears and weird things like harassing our users on social media) with no attempt to even be stealthy about it. I don't even get why they bothered--users see through that stuff, putting so much bad energy and nastiness into the world is such a waste of effort and human capital.
Why would you think users would see through that stuff? The app developer may care. I don't see any reason why any users would put in the effort to investigate the authenticity of reviews on some random app.
