Consider the following situation:
Q: I only have a limited time budget to read books. In order to learn as much as possible about a subject XYZ, which books should I read? (I can't read them all due to lack of time).
A: Obviously, I do not know the books yet. So I can't decide based on knowledge. But I may have reputation information available about the authors (how I liked their books in the past, or, how people who I respect a lot liked their books in the past). Using this reputation information helps me in making a decision. There is no guaranty that my decision will be right, but it improves my chances of making a good (or, at least reasonable) decision. In other words: Reputation information helps me in maximizing the expected outcome (what I will have learned) of my limited investment of resources (time).
Reputation is knowledge about the past. It is NOT knowledge about the present or about the future. It may serve to make an educated assumption/estimate/guess about the present or the future. Hence, reputation represents an expectation about the present or about the future, but there is no guaranty that this expectation is correct (but it sould at least be reasonable, based on past experience).