“Do you write a review for every book you read or only review copies from publishers?”
It's a given that all the books I receive from publishers get reviewed eventually... otherwise they'd stop sending me books.
As for books that I buy or rent from the library, I review them if I have the time and desire. Extra time is often in low supply around my house, but I will make time if I feel the book warrants the effort. If I find an amazing book, I'll definitely share how much I enjoyed it. If the book is disappointing, I'll warn others to rent before buying.
What about you?