In my opinion, if a product in question has trouble fulfilling its destiny as advertised, but still has other features that make it worth considering, it will get a 2-star (AKA 'fair') rating from this reviewer.  However if a product cannot fulfill its promised capability, and simultaneously makes me want to throw it out of a 20 story window during testing, then it will get a one star (AKA 'poor') rating.  For the record, the other opportunity for a one-star rating is if the product severely damages otherwise functional equipment it is connected to. 

For the first example of a one-star rating in my over five years of reviews, click here to go to pcmag.com