Friends don’t give friends four stars
The creator economy runs on people but it is powered by computers and computers are binary. They have a really hard time with nuance.
If your friend has written a book, or is marketing a product, you might want to help them get the word out by leaving a review. You might also think they could have done better and not really believe in your heart of hearts that it is worthy of five stars.
What should you do?
If you honestly want to be helpful in getting the word out you need to start thinking like a computer and realize that this is commerce not a classroom. Deliver your critique to them privately but if you want to help their venture, leave five stars.
To an algorithm five stars is a recommendation, four stars is a warning.
Algorithms see anything less than five as saying, “Something is wrong here.” And your four star review actually works to bury your friend’s work.
I cannot speak for everyone but I would rather receive a well formed private critique and no review rather than a four star review that tells our robot overlords that my work is sub-standard.