I haven't seen this mentioned elsewhere, so I'll get it on the record here.
Prior to the introduction of in-app purchases there was a difference between reviews of "free" (ad-supported) apps and honest apps. Reviews of free apps were worthless; a mix of fly-by reviews and scan reviews paid for by app revenue. Reviews of honest, pay for what you get, apps were useful. It was relatively costly to pay for a large number of favorable reviews.
With in-app purchasing freemium model apps though, the reviews ad-supported app quality - worth nothing.