I get the product and test it out or if I personally can’t test it I find a person, friend or family member that is willing to try it out for me.
I also gather real true testimonials if i don’t have any experience using the product that i am reviewing .
Then I interview them or take my own thoughts and results to write a comprehensive review on the product giving you all the details, the good points, bad points and my thoughts on whether its worth buying or not.