If it’s truly a friend, then I might let the friend know of my less than stellar experience and see if (s)he has any comments. (S)he may try to remedy my concerns before I “go to print” which, if I’m notified could either make me go back for a second chance, or include in my reivew that ownership was responsive to my criticism and made subsequent changes.
 
A bad review could damage a friendship. If I care about the friendship, I would do what a friend would do. give him/her a heads up and see if (s)he would like to work through it, before my review gets posted/printed.
 
That’s being a friend, and a fair reviewer.