Agents predicted market changes and trends. They looked at what was already out, what was slated to be released, what was already selling, what wasn’t, what was saturated, etc. Then, they used that data to maneuver their authors around the sales minefield. Still do to the best of their abilities. Yet, there often are REAL reasons a book isn’t selling and it isn’t the reader’s fault. It’s all on the book and the author.