To put it in very non-scientific terms: people love an underdog. If your business is flourishing and someone leaves a negative review, eh, you're doing good. But if I see someone do a 3-star for some corner bodega that just happens to be one that I visit - oh, I must right this wrong with a 5-star review.

It's impossible for my instincts not to kick in and push me into rooting for the 'little guy' or someone who's been unfairly wronged. (Whether they were wronged fairly or unfairly is a matter my instincts leave for later.)