I gave an honest review of some $30 bluetooth headphones. I gave it a 3 star, and listed my complaints. The company reached out to me, offered to send me 2 more, for free, of their newer and better model, if I just adjusted my review to all stars. That was when I stopped believing them.

This is so common that I considered creating a browser extension to convert/normalize the the min and max values on a page into a 5-star rating. When the lowest rating of items on the page is 4.2, 4.2 would displayed as 1.