[margalabargala]

Firstly, I said "Western" not "developed", you need to calibrate your quip detector lest you become what you dislike.

Secondly, while it's possible to construct a private party transaction in the US where this is fine, if the person spending the duffel bag acquired the money illegally, you the seller are liable if you should have known. "Willful blindness" when accepting illegal proceeds makes you liable too. See 18 U.S.C. § 1957

Maybe I misspoke by saying you would be liable for laundering specifically, but certainly accepting that money is a crime if you have any reason to think it was ill-gotten. And that's a huge risk that no one wants to take on.