Good point about the return if the store's policies allow it.Not sure if this has already been brought up, but in terms of the sign-the-new-book rule, what about returns? Say someone buys a new book, and gets another book signed, there's no real way to stop someone from returning the new book (there really isn't). Granted, a store could play the odds, and perhaps statistically returns would be low, but usually when someone sets up a rule like this it is done because of the qualitative logic of the rule itself, not the statistical reality of it (I'm guessing, anyway).
Plus, I would think the idea would be that the new book is actually in the hands of buyers. The hope is the buyers will read the book and enjoy it. Generate word of mouth. And then watch/read whatever derivative projects come of it (book sequel, streaming series, comic book adaptation, etc.).
However, please understand, I do sympathize. I understand why someone would want another book signed. Also, if I don't understand something about the situation that would make my reply illogical relative to the parameters in place, please forgive.