I feel that the number one thing that prevents me from recommending a book to someone else is that the person does not like to read. More of my family and friends do not read, than do. Those family and friends that do read do not read as much as I do. My dad and I recommend books to each other, my daughter in-law Christina and I share books, my older sister JoAnn and I share books. I am in a charge of the book club at my Church and I recommend books to them.
Poor writing, poor theology, explicit sex and profanity, inappropriate subject matter, these are issues that I've not come across yet in the Christian fiction and Christian non fiction books that I've read and then recommended. When I recognize the authors name and read the back cover of the book, it is almost never that I will then read the book and be offended by its content.
Secular books are a different story, I can think of only a few times that I've been disappointed and shocked by its content enough that not only did I not recommend the book, but I did not finish the book myself.
I have a few friends that are not in the least bit interested in reading Christian fiction or Christian non fiction, it is their choice, and I will not recommend a book from those categories to them. They know that I read from these genre's because I talk about some of the books, they listen attentively and may ask a question, but I'm not going to be "pushy" in trying to talk them in to reading the book.