Can you as the publisher or as the agent guarantee that my book will sell?
A. There is no guarantee.
No Agent, Publisher, Bookstore clerk or wholesaler will guarantee that your book will sell a certain number of copies.
This would be like us asking you to make us a guarantee that your book will sell so many copies.
This is an impossible to know, since there are 3.5 million book titles plus that are published each year.
Also the only way that any authors' book will sell, is based on what the author is willing to do on their part as being a published author.