Wiktionary
sell down
vb. 1 (context intransitive British business English) To become less by being sold. 2 (context transitive British business English) To reduce by selling.
Usage examples of "sell down".
One of those black plastic garbage cans like they sell down at the Tru-Value in town.
They had been hauling what they didn't sell down to the tunnels beneath the tower, where it sat, covered in sheets.
Do you think things like that ever happen in real life, or only in those cheap newspapers they sell down to the grocery?