This implies that everyone's perception of "value" is the same. And that everyone's perception of "fairness" is the same. In this example there is no such thing as "the true value of the book" because what is considered "the value of the book" is in the mind of the consumer AND the mind of the seller, and different people will put different value on it. Thus profit is not inherently unethical, because the bookseller is not taking advantage of the customer, the customer is perfectly willing to pay what they consider the "value" of that book to be.

Discrepancies in perception of value come from a number of things, personal preference (someone who loves reading will value books higher than someone who can't read for example), as well as personal talents and skills. Someone who is good at making books, and enjoys the work, will not consider it onerous to do so, and thus they won't "value" the work of making the book at the same level that someone who doesn't have any skill at making books, for whom making a book would take 100x the effort than the person who is good at it. Whereas the customer might be bad at making books, but good at idk, being a dentist.

This inherent discrepancy between personal preference, personal abilities/skills, and different perceptions of "value" is what leads to profit and "surplus". Even if in a perfectly communist society you abolished profit, or abolished private/personal property, you would not ever be able to change the fact that humans have different preferences, skill levels, perceptions of value etc.