If money laundering is happening via book deals and foreign aid, then it works like this:
USA taxpayer money Foreign aid to Country X > Country X's dictator "donates" (kickback) money to Bertelsmann Stiftung, a German foundation that has controlling ownership in Random House Publishing > Random House Publishing gives book deal advances to dirty politicians, who have someone else write them a book that nobody is interested in.
Who buys the books? Foreign governments? Foundations? Nobody?
The Mohn family owns/controls Random House.
The money could easily go in circles through foreign entities (governments, private foundations, Iranian cash payments, whatever), and end up in "clean" deals via books, art, etc.