How are efforts measured?

While writing a “book” I interview various people and each of them share their views.

After the book is compiled and published revenue is generated.

Here would it be ethical for the author and publisher to keep all the money for oneself?

Again, if money is to be paid back to the people who participated in the interview process taking time from their busy schedule how are they to be compensated? How are their efforts to be measured?

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