If I think I will listen to the book a second time or if I just really liked it, or if it is a small author, I keep it. But some books are just not very good and I don't think I should be punished for taking a chance on them. Any book I hold onto for more than one calendar year is locked to my account forever, and Audible limits me to like 3 trade-in's a year. So it's not that bad.