Would you sell for cash?

Sounds very fishy to me... "yah, an employee of mine just so happens to be in your area and also happens to have a huge wad of cash with him... and he has nothing better to do, but to spend his time tracking you down to buy something that''s not even for him".  Who travels with a lot of cash anyways, besides drug dealers and strippers?  Hard pass.

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. 

I’m sure there are drug dealers and strippers with PayPal, checks, credit cards, etc. Cash too.

We could drive ourselves crazy wondering where the money ‘came from’ to pay us for both goods and services.

Im in the design/build business. Never ceases to amaze how many builders and contractors/subcontractors love cash. Many dislike having to fill-out 1099’s. I usually ask for a check regardless.

One way might be to:

Do the transaction during the business day at a bank-- yours if possible, and see if the bank will verify the legitimacy of the currency being used before you hand over the amp. (You can have that done discretely by having the buyer’s employee hand the cash to a bank employee for counting, without necessarily mentioning the verification part). I would talk with your bank before you suggest that though, to make sure they can do this.

Document the terms of the deal and have it signed for. Last thing you want is a tough guy looking for his cash back for whatever reason.