I think they should be able to tell apart from people's purchasing history if they are "organic" buyers [normal people's consumption patterns of goods] or something organized to curry favorable reviews.

Sure someone could get paid to review an item and also be an avid consumer of a product, but in that case it would seem they believe in the item.

Imagine someone buys eneloop over and over, never offer a review, then purchases a no-name brand, gives rave reviews and goes back to buying eneloop again.