Is money earned from selling books, some of which are printed from unauthorized electronic copies, with the customers' knowledge of that, considered unlawful money?

There is no harm in working as a representative for a store that sells physical books. Your work is not affected by the fact that some books might be photocopied, as long as you do not know whether the photocopier obtained permission or not, or whether the owner prohibits its copying. A mere possibility is not taken into consideration, because what is unknown is legally considered as non-existent.