How do I know? Well... they have done it in the past many times. Go read some of the reviews on games with low critic, but high user ratings. Fraud reviews aren't anything new.
Well, a difference between pro reviews and user reviews can have many reasons. The most likely one is that games get updated over time and user reviews react to that while pro reviews are only made at release. Another fact is of course that there is often a much higher user base for user reviews than for pro reviews. And then there is the "herd instinct" in both positive and negative directions which applies on internet users even more than on pro reviewers...
I actually never read a real "fraud" review before which was such an obvious scam. Of course I've read a lot of reviews that I myself thought which were lacking in both writing quality and content but at least the reviewers seemed to get the basic facts rights (which is not the case here)...
