This video goes over what "verified purchase reviews" are and how they are useful. Below is the link to install the additional app mentioned in the video:

Link to install the Amazon Mobile App

The main thing to remember is that if there is an item that has no sales rank, but has reviews, you should check to see if any of the reviews are verified purchase reviews. If there are verified purchase reviews, then you should buy the item as long as it meets your ROI guidelines.