I get to review a book for a UP on the exact topic of my own last book. Watch for me to be totally objective.
All kidding aside, I had to think for a few minutes before saying yes. Obviously I have a stake here. If the person does not cite me then I will have to say that. If there is disagreement, I will negotiate that.
But really, it is a good chance for me to practice not being defensive or territorial, and to put aside anything personal. I actually can be objective, in the sense that if the book does something I don't do, or addresses the topic in another way, all the more power to this scholar. I shouldn't even have to have a strong attachment to my own ideas. How does that benefit me?