IMO, it is not fair for someone to review a product they know nothing about. That is misleading the reader and costing your creditability.

I only review a product that I personally own and use unless it is a place I have been to, or services I have used. I have several products that I bought recently, but have not tried yet. I will normally write a review on it after using it for a good month (depending what the product is) so I know the pros and cons of it. I think this is a good time frame to use the product to see if it is going to break or tear up on you. Also, say, I wrote a review and sometime later the product is not what it cracks up to be, or breaks, recalled, etc. Then I would update my review to that effect. 

If I used a product of a family member or a friend, I probably would not do a review on it unless I was very familiar with it or I could borrow it for a couple of weeks to try it out.