NO!
DC absolutely WILL flip out and confiscate. Their gun laws are far beyond draconian. And they are well known to confiscate first, ask questions later.
For example, their chief of police once said:
"The federal FOPA law doesn't apply in DC; you cannot drive through with a gun; you must go around."
His statement was false and illegal, of course. But no one challenged it.
You don't want that mess on your hands.
Ask the sell to provide an address outside DC, or offer to refund his money.