Cash is a euphemism for Federal Reserve Notes. FRN are created from nothing and loaned into existence. That is why it says right on the face, Federal Reserve NOTE. A note is a loan, an IOU. Long ago this made sense, the note was redeemable for gold. Now it is an IOU nothing. Also opens you up to money laundering and reporting requirements. I would insist on real money. If the buyer is legit he will pay legit money. Send him your bitcoin address.
If you think that's a joke, I'm not the one questioning "This note is legal tender for all debts public and private." Dude is afraid to use US legal tender.