I agree there is a strong subliminal effect when there are over 100 reviews on a book, BUT if they're all 4- and 5-star reviews, I discount them.
Amazon must do something specific regarding the First Reads audience to get so many and to have perfect timing, too, because ordinarily a pre-release title can't have a review. What are the odds that 700 people remembered to post their review on the exact release day? Very poor, I'd say, without some manipulation/coordination by Amazon. Hurray for those authors.
Yes, it could be manipulation by the author, but then that author must have an extremely large and obedient ARC team. Possible, of course.